Add real numbers with the same and different signs
Subtract real numbers with the same and different signs
Simplify combinations that require both addition and subtraction of real numbers.
Multiply and divide real numbers
Multiply two or more real numbers.
Divide real numbers
Simplify expressions with both multiplication and division
Simplify expressions with real numbers
Recognize and combine like terms in an expression
Simplify compound expressions with real numbers
Simplify expressions with fraction bars, brackets, and parentheses
Use the distributive property to simplify expressions with grouping symbols
Simplify expressions containing absolute values
Some important terminology to remember before we begin is as follows:
integers: counting numbers like 1, 2, 3, etc., including negatives and zero
real number: fractions, negative numbers, decimals, integers, and zero are all real numbers
absolute value: a number's distance from zero; it's always positive. ∣−7∣=7
sign: this refers to whether a number is positive or negative, we use + for positive (to the right of zero on the number line) and − for negative (to the left of zero on the number line)
difference: the result of subtraction
sum: the result of addition
The ability to work comfortably with negative numbers is essential to success in algebra. For this reason we will do a quick review of adding, subtracting, multiplying and dividing integers. Integers are all the positive whole numbers, zero, and their opposites (negatives). As this is intended to be a review of integers, the descriptions and examples will not be as detailed as a normal lesson.
Adding and Subtracting Real Numbers
When adding integers we have two cases to consider. The first case is whether the signs match (both positive or both negative). If the signs match, we will add the numbers together and keep the sign.
If the signs don’t match (one positive and one negative number) we will subtract the numbers (as if they were all positive) and then use the sign from the larger number. This means if the larger number is positive, the answer is positive. If the larger number is negative, the answer is negative.
To add two numbers with the same sign (both positive or both negative)
Add their absolute values (without the + or − sign)
Give the sum the same sign.
To add two numbers with different signs (one positive and one negative)
Find the difference oftheir absolute values. (Note that when you find the difference of the absolute values, you always subtract the lesser absolute value from the greater one.)
Give the sum the same sign as the number with the greater absolute value.
Example
Find 23–73.
Answer: You can't use your usual method of subtraction because 73 is greater than 23. Rewrite the subtraction as adding the opposite.
23+(−73)
The addends have different signs, so find the difference of their absolute values.
∣23∣=23and∣−73∣=7373−23=50
Since ∣−73∣>∣23∣, the final answer is negative.
Answer
23–73=−50
Another way to think about subtracting is to think about the distance between the two numbers on the number line. In the example below, 382 is to the right of 0 by 382 units, and −93 is to the left of 0 by 93 units. The distance between them is the sum of their distances to 0: 382+93.
Example
Find 382–(−93).
Answer: You are subtracting a negative, so think of this as taking the negative sign away. This becomes an addition problem. −93 becomes +93
382+93=475
Answer
382–(−93)=475
The following video explains how to subtract two signed integers.
https://youtu.be/ciuIKFCtWWU
Example
Find −73−76+72
Answer: Add the first two and give the result a negative sign:
Since the signs of the first two are the same, find the sum of the absolute values of the fractions
Since both numbers are negative, the sum is negative. If you owe money, then borrow more, the amount you owe becomes larger.
−73=73 and −76=76
73+76=79−73−76=−79
Now add the third number. The signs are different, so find the difference of their absolute values.
−79=79 and 72=72
79−72=77
Since 7−9>72, the sign of the final sum is the same as the sign of −79.
−79+72=−77
Answer
−73+(−76)+72=−77
In the following video you will see an example of how to add three fractions with a common denominator that have different signs.
https://youtu.be/P972VVbR98k
Example
Evaluate 27.832+(−3.06). When you add decimals, remember to line up the decimal points so you are adding tenths to tenths, hundredths to hundredths, and so on.
Answer: Since the addends have different signs, subtract their absolute values.
27.832−3.0624.772
∣−3.06∣=3.06
The sum has the same sign as 27.832 whose absolute value is greater.
Answer
27.832+(−3.06)=24.772
In the following video are examples of adding and subtracting decimals with different signs.
https://youtu.be/3FHZQ5iKcpI
Multiplying and Dividing Real Numbers
Multiplication and division are inverse operations, just as addition and subtraction are. You may recall that when you divide fractions, you multiply by the reciprocal. Inverse operations "undo" each other.
Multiply Real Numbers
Multiplying real numbers is not that different from multiplying whole numbers and positive fractions. However, you haven't learned what effect a negative sign has on the product.
With whole numbers, you can think of multiplication as repeated addition. Using the number line, you can make multiple jumps of a given size. For example, the following picture shows the product 3⋅4 as 3 jumps of 4 units each.
So to multiply 3(−4), you can face left (toward the negative side) and make three “jumps” forward (in a negative direction).
The product of a positive number and a negative number (or a negative and a positive) is negative.
The Product of a Positive Number and a Negative Number
To multiply a positive number and a negative number, multiply their absolute values. The product is negative.
Example
Find −3.8(0.6).
Answer: Multiply the absolute values as you normally would. Place the decimal point by counting place values. 3.8 has 1 place after the decimal point, and 0.6 has 1 place after the decimal point, so the product has 1+1 or 2 places after the decimal point.
3.8×0.62.28
The product of a negative and a positive is negative.
Answer
−3.8(0.6)=−2.28
The following video contains examples of how to multiply decimal numbers with different signs.
https://youtu.be/7gY0S3LUUyQ
The Product of Two Numbers with the Same Sign (both positive or both negative)
To multiply two positive numbers, multiply their absolute values. The product is positive.
To multiply two negative numbers, multiply their absolute values. The product is positive.
Example
Find (−43)(−52)
Answer: Multiply the absolute values of the numbers. First, multiply the numerators together to get the product's numerator. Then, multiply the denominators together to get the product's denominator. Rewrite in lowest terms, if needed.
(43)(52)=206=103
The product of two negative numbers is positive.
Answer
(−43)(−52)=103
The following video shows examples of multiplying two signed fractions, including simplification of the answer.
https://youtu.be/yUdJ46pTblo
To summarize:
positive ⋅ positive: The product is positive.
negative ⋅ negative: The product is positive.
negative ⋅ positive: The product is negative.
positive ⋅ negative: The product is negative.
You can see that the product of two negative numbers is a positive number. So, if you are multiplying more than two numbers, you can count the number of negative factors.
Multiplying More Than Two Negative Numbers
If there are an even number (0, 2, 4, ...) of negative factors to multiply, the product is positive.
If there are an odd number (1, 3, 5, ...) of negative factors, the product is negative.
Example
Find 3(−6)(2)(−3)(−1).
Answer: Multiply the absolute values of the numbers.
3(6)(2)(3)(1)18(2)(3)(1)36(3)(1)108(1)108
Count the number of negative factors. There are three (−6,−3,−1).
3(−6)(2)(−3)(−1)
Since there are an odd number of negative factors, the product is negative.
Answer
3(−6)(2)(−3)(−1)=−108
The following video contains examples of multiplying more than two signed integers.
https://youtu.be/rx8F9SPd0HE
Divide Real Numbers
You may remember that when you divided fractions, you multiplied by the reciprocal. Reciprocal is another name for the multiplicative inverse (just as opposite is another name for additive inverse).
An easy way to find the multiplicative inverse is to just “flip” the numerator and denominator as you did to find the reciprocal. Here are some examples:
The reciprocal of 94 is 49because 94(49)=3636=1.
The reciprocal of 3 is 31 because 13(31)=33=1.
The reciprocal of −65 is 5−6 because −65(−56)=3030=1.
The reciprocal of 1 is 1 as 1(1)=1.
When you divided by positive fractions, you learned to multiply by the reciprocal. You also do this to divide real numbers.
Think about dividing a bag of 26 marbles into two smaller bags with the same number of marbles in each. You can also say each smaller bag has one half of the marbles.
26÷2=26(21)=13
Notice that 2 and 21 are reciprocals.
Try again, dividing a bag of 36 marbles into smaller bags.
Number of bags
Dividing by number of bags
Multiplying by reciprocal
3
336=12
36(31)=336=312(3)=12
4
436=9
36(41)=436=49(4)=9
6
636=6
36(61)=636=66(6)=6
Dividing by a number is the same as multiplying by its reciprocal. (That is, you use the reciprocal of the divisor, the second number in the division problem.)
Example
Find 28÷34
Answer: Rewrite the division as multiplication by the reciprocal. The reciprocal of 34 is 43.
28÷34=28(43)
Multiply.
128(43)=428(3)=44(7)(3)=7(3)=21
Answer
28÷34=21
Now let's see what this means when one or more of the numbers is negative. A number and its reciprocal have the same sign. Since division is rewritten as multiplication using the reciprocal of the divisor, and taking the reciprocal doesn’t change any of the signs, division follows the same rules as multiplication.
Rules of Division
When dividing, rewrite the problem as multiplication using the reciprocal of the divisor as the second factor.
When one number is positive and the other is negative, the quotient is negative.
When both numbers are negative, the quotient is positive.
When both numbers are positive, the quotient is positive.
Example
Find 24÷(−65).
Answer: Rewrite the division as multiplication by the reciprocal.
24÷(−65)=24(−56)
Multiply. Since one number is positive and one is negative, the product is negative.
124(−56)=−5144
Answer
24÷(−65)=−5144
Example
Find 4(−32)÷(−6)
Answer: Rewrite the division as multiplication by the reciprocal.
14(−32)(−61)
Multiply. There is an even number of negative numbers, so the product is positive.
3(6)4(2)(1)=188
Write the fraction in lowest terms.
Answer
4(−32)÷(−6)=94
The following video explains how to divide signed fractions.
https://youtu.be/OPHdadhDJoI
Remember that a fraction bar also indicates division, so a negative sign in front of a fraction goes with the numerator, the denominator, or the whole fraction: −43=4−3=−43.
In each case, the overall fraction is negative because there's only one negative in the division.
The following video explains how to divide signed fractions.
https://youtu.be/OPHdadhDJoI
Simplify Expressions With Real Numbers
Some important terminology before we begin:
operations/operators: In mathematics we call things like multiplication, division, addition, and subtraction operations. They are the verbs of the math world, doing work on numbers and variables. The symbols used to denote operations are called operators, such as +,−,×,÷. As you learn more math, you will learn more operators.
term: Examples of terms would be 2x and −23 or a3. Even lone integers can be a term, like 0.
expression: A mathematical expression is one that connects terms with mathematical operators. For example 21+(22)−9÷76 is an expression.
Combining Like Terms
One way we can simplify expressions is to combine like terms. Like terms are terms where the variables match exactly (exponents included). Examples of like terms would be 5xy and −3xy or 8a2b and a2b or −3 and 8. If we have like terms we are allowed to add (or subtract) the numbers in front of the variables, then keep the variables the same. As we combine like terms we need to interpret subtraction signs as part of the following term. This means if we see a subtraction sign, we treat the following term like a negative term. The sign always stays with the term.
This is shown in the following examples:
Example
Combine like terms: 5x−2y−8x+7y
Answer:
The like terms in this expression are:
5x and −8x
−2y and −7y
Note how we kept the sign in front of each term.
Combine like terms:
5x−8x=−3x
−2y−7y=−9y
Note how signs become operations when you combine like terms.
Simplified Expression:
5x−2y−8x+7y=−3x−9y
In the following video you will be shown how to combine like terms using the idea of the distributive property. Note that this is a different method than is shown in the written examples on this page, but it obtains the same result.
https://youtu.be/JIleqbO8Tf0
Example
Combine like terms: x2−3x+9−5x2+3x−1
Answer:
The like terms in this expression are:
x2 and −5x2
−3x and 3x
9 and −1
Combine like terms:
x2−5x2=−4x2−3x+3x=09−1=8
In the video that follows, you will be shown another example of combining like terms. Pay attention to why you are not able to combine all three terms in the example.
https://youtu.be/b9-7eu29pNM
Simplify Compound Expressions With Real Numbers
In this section, we will use the skills from the last section to simplify mathematical expressions that contain many grouping symbols and many operations. We are using the term compound to describe expressions that have many operations and many grouping symbols. More care is needed with these expressions when you apply the order of operations. Additionally, you will see how to handle absolute value terms when you simplify expressions.
Example
Simplify 32+25−[3+(2⋅(−6))]
Answer: This problem has brackets, parentheses, fractions, exponents, multiplication, subtraction, and addition in it.
Grouping symbols are handled first. The parentheses around the −6 aren’t a grouping symbol; they are simply making it clear that the negative sign belongs to the 6. Start with the innermost set of parentheses that are a grouping symbol. In this example, the innermost set of parentheses would be in the numerator of the fraction, (2⋅(−6)). Begin working out from there. (The fraction line acts as a type of grouping symbol, too; you simplify the numerator and denominator independently, and then divide the numerator by the denominator at the end.)
32+25−[3+(2⋅(−6))]32+25−[3+(−12)]
Add 3 and −12, which are in brackets, to get −9.
32+25−[3+(−12)]32+25−[−9]
Subtract 5–[−9]=5+9=14.
32+25−[−9]32+214
The top of the fraction is all set, but the bottom (denominator) has remained untouched. Apply the order of operations to that as well. Begin by evaluating 32=9.
32+2149+214
Now add. 9+2=11.
9+2141114
Answer
32+25−[3+(2⋅(−6))]=1114
The video that follows contains an example similar to the written one above. Note how the numerator and denominator of the fraction are simplified separately.
https://youtu.be/xIJLq54jM44
The Distributive Property
Parentheses are used to group or combine expressions and terms in mathematics. You may see them used when you are working with formulas, and when you are translating a real situation into a mathematical problem so you can find a quantitative solution.
Combo Meal Distributive Property
For example, you are on your way to hang out with your friends, and call them to ask if they want something from your favorite drive-through. Three people want the same combo meal of 2 tacos and one drink. You can use the distributive property to find out how many total tacos and how many total drinks you should take to them.
The distributive property allows us to explicitly describe a total that is a result of a group of groups. In the case of the combo meals, we have three groups of ( two tacos plus one drink). The following definition describes how to use the distributive property in general terms.
The Distributive Property of Multiplication
For all real numbers a, b, and c, a(b+c)=ab+ac.
What this means is that when a number multiplies an expression inside parentheses, you can distribute the multiplication to each term of the expression individually.
To simplify 3(3+y)−y+9, it may help to see the expression translated into words:
multiply three by (the sum of three and y), then subtract y, then add 9
To multiply three by the sum of three and y, you use the distributive property -
3(3+y)−y+9=3⋅3+3⋅y−y+9=9+3y−y+9
Now you can subtract y from 3y and add 9 to 9.
9+3y−y+9=18+2y
The next example shows how to use the distributive property when one of the terms involved is negative.
Example
Simplify a+2(5−a)+3(a+4)
Answer:
This expression has two sets of parentheses with variables locked up in them. We will use the distributive property to remove the parentheses.
a+2(5−a)+3(a+4)=a+2⋅5−2⋅a+3⋅a+3⋅4
Note how we placed the negative sign that was on b in front of the 2 when we applied the distributive property. When you multiply a negative by a positive the result is negative, so 2⋅−a=−2a. It is important to be careful with negative signs when you are using the distributive property.
a+2⋅5−2⋅a+3⋅a+3⋅4=a+10−2a+3a+12=2a+22
We combined all the terms we could to get our final result.
Answer
a+2(5−a)+3(a+4)=2a+22
Absolute Value
Absolute value expressions are one final method of grouping that you may see. Recall that the absolute value of a quantity is always positive or 0.
When you see an absolute value expression included within a larger expression, treat the absolute value like a grouping symbol and evaluate the expression within the absolute value sign first. Then take the absolute value of that expression. The example below shows how this is done.
Example
Simplify 2∣3⋅1.5∣−(−3)3+∣2−6∣.
Answer: This problem has absolute values, decimals, multiplication, subtraction, and addition in it.
Grouping symbols, including absolute value, are handled first. Simplify the numerator, then the denominator.
Evaluate ∣2–6∣.
2∣3⋅1.5∣−(−3)3+∣2−6∣2∣3⋅1.5∣−(−3)3+∣−4∣
Take the absolute value of ∣−4∣.
2∣3⋅1.5∣−(−3)3+∣−4∣2∣3⋅1.5∣−(−3)3+4
Add the numbers in the numerator.
2∣3⋅1.5∣−(−3)3+42∣3⋅1.5∣−(−3)7
Now that the numerator is simplified, turn to the denominator.
Evaluate the absolute value expression first. 3⋅1.5=4.5, giving
2∣3⋅1.5∣−(−3)72∣4.5∣−(−3)7
The expression “2∣4.5∣” reads “2 times the absolute value of 4.5.” Multiply 2 times 4.5.
2∣4.5∣−(−3)79−(−3)7
Subtract.
9−(−3)7127
Answer
2∣3⋅1.5∣−3(−3)3+∣2−6∣=127
The following video uses the order of operations to simplify an expression in fraction form that contains absolute value terms. Note how the absolute values are treated like parentheses and brackets when using the order of operations.
https://youtu.be/6wmCQprxlnU
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Ex 2: Subtracting Integers (Two Digit Integers).Authored by: James Sousa (Mathispower4u.com) for Lumen Learning.License: CC BY: Attribution.
Find the Sum and Difference of Three Signed Fractions (Common Denom).Authored by: James Sousa (Mathispower4u.com) for Lumen Learning.License: CC BY: Attribution.
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Unit 9: Real Numbers, from Developmental Math: An Open Program.Provided by: Monterey Institute of Technology and EducationLocated at: https://www.nroc.org/.License: CC BY: Attribution.
Ex: Multiplying Three or More Integers.Authored by: James Sousa (Mathispower4u.com) for Lumen Learning.License: CC BY: Attribution.
Ex: Multiplying Signed Fractions .Authored by: James Sousa (Mathispower4u.com) for Lumen Learning.License: CC BY: Attribution.
Ex 1: Dividing Signed Fractions.Authored by: James Sousa (Mathispower4u.com) for Lumen Learning.License: CC BY: Attribution.
Ex 2: Combining Like Terms.Authored by: James Sousa (Mathispower4u.com) for Lumen Learning.License: CC BY: Attribution.
Simplify an Expression in the Form: a-b+c*d.Authored by: James Sousa (Mathispower4u.com) for Lumen Learning.License: CC BY: Attribution.
Simplify an Expression in the Form: a*1/b-c/(1/d).Authored by: James Sousa (Mathispower4u.com) for Lumen Learning.License: CC BY: Attribution.
Simplify an Expression in the Form: (a+b)^2+c*d.Authored by: James Sousa (Mathispower4u.com) for Lumen Learning.License: CC BY: Attribution.
Simplify an Expression in Fraction Form.Authored by: James Sousa (Mathispower4u.com) for Lumen Learning.License: CC BY: Attribution.
Simplify an Expression in Fraction Form with Absolute Values.Authored by: James Sousa (Mathispower4u.com) for Lumen Learning.License: CC BY: Attribution.