Question

Xiao's teacher asked him to rewrite the sum 60+90 the product of the GCF of the two numbers and a sum. Axial wrote 3(20+30). What mistake did axial make? How should he have written the sum?

Answer 1

60 + 90

GCF = 30

(30 * 2) + (30 * 3) = 30(2 + 3) <== the correct way

The mistake Axial made was he did not pick the greatest common factor...he picked 3 instead of 30.

Answer 2

Given expression,

60 + 90,

∵ 60 = 2 × 2 × 3 × 5,

90 = 2 × 3 × 3 × 5,

Thus, GCF( 60, 90) = 2 × 3 × 5 = 30,

So, we can write,

60 = 30 × 2 and 90 = 30 × 3,

∴ 60 + 90 = 30 × 2 + 30 × 3 = 30( 2 + 3 )

Hence, he had the mistake in finding the GCF of 60 and 90 i.e. he should write 30( 2 + 3 ) instead of 3(20+30)