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Study Guides > ALGEBRA / TRIG I

Summary: Finding Multiples and Factors

Key Concepts

Divisibility Tests
A number is divisible by
22 if the last digit is 0,2,4,6,0, 2, 4, 6, or 88
33 if the sum of the digits is divisible by 33
55 if the last digit is 55 or 00
66 if divisible by both 22 and 33
1010 if the last digit is 00
  • Factors If ab=ma\cdot b=m , then aa and bb are factors of mm , and mm is the product of aa and bb .
  • Find all the factors of a counting number.
    1. Divide the number by each of the counting numbers, in order, until the quotient is smaller than the divisor.
      1. If the quotient is a counting number, the divisor and quotient are a pair of factors.
      2. If the quotient is not a counting number, the divisor is not a factor.
    2. List all the factor pairs.
    3. Write all the factors in order from smallest to largest.
  • Determine if a number is prime.
    1. Test each of the primes, in order, to see if it is a factor of the number.
    2. Start with 22 and stop when the quotient is smaller than the divisor or when a prime factor is found.
    3. If the number has a prime factor, then it is a composite number. If it has no prime factors, then the number is prime.

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