1.
If you missed this problem, review the following example.
Identify each number as prime or composite:
- 83
- 77
Answer:
Solution:
1. Test each prime, in order, to see if it is a factor of 83 , starting with 2, as shown. We will stop when the quotient is smaller than the divisor.
Prime |
Test |
Factor of 83? |
2 |
Last digit of 83 is not 0,2,4,6,or8. |
No. |
3 |
8+3=11, and 11 is not divisible by 3. |
No. |
5 |
The last digit of 83 is not 5 or 0. |
No. |
7 |
83÷7=11.857… |
No. |
11 |
83÷11=7.545… |
No. |
We can stop when we get to
11 because the quotient
(7.545…) is less than the divisor.
We did not find any prime numbers that are factors of
83, so we know
83 is prime.
2. Test each prime, in order, to see if it is a factor of
77.
Prime |
Test |
Factor of 77? |
2 |
Last digit is not 0,2,4,6,or 8. |
No. |
3 |
7+7=14, and 14 is not divisible by 3. |
No. |
5 |
the last digit is not 5 or 0. |
No. |
7 |
77÷11=7 |
Yes. |
Since
77 is divisible by
7, we know it is not a prime number. It is composite.