Question

Which is NOT a common factor of 20 and 36?

Options

• 1

• 2

• 4

• 5

Answer 1

5

Explanation:

• Factors of 20: 1, 2, 4, 5, 10, 20

• Factors of 36: 1, 2, 3, 4, 6, 9, 12, 18, 36

The only number in 20’s list but not in 36’s is 5, so 5 is not a common factor.

or

5 is not a common factor of 20 and 36 because:

• 20 ÷ 5 = 4 (so 5 is a factor of 20)

• 36 ÷ 5 = 7.2 (not a whole number, so 5 is not a factor of 36)

Therefore, 5 is not shared by both numbers, making it the correct answer.