Exercises: Factor Pairs, Multiples, Primes, and Composites
Work through each section in order. When a problem asks for all factor pairs, test every
number in order starting from 1, and stop once the factors begin to repeat.
Recall / Warm-Up
Compute 24 / 4.
Compute 5 x 9.
Compute 8 x 9.
Fluency Practice
How many factor pairs does 28 have?
Find all factor pairs of 40 by testing every number in order: 1 x 40, 2 x ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ,
4 x ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ , 5 x ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ .
Is 6 a factor of 42?
Yes -- 42 / 6 = 7 with no remainder.
No -- 42 / 6 leaves a remainder.
Is 45 a multiple of 8?
No -- 45 / 8 = 5 remainder 5, not a whole number.
Yes -- 45 / 8 is a whole number.
How many factor pairs does 48 have?
Use the digit-sum rule to check whether 84 is divisible by 3. Digit sum: 8 + 4 =
̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ . Is 84 divisible by 3? Answer ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ (yes or no).
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