F.1 Maths 請幫忙，Thanks

If A is greater than B by 25%, A = 1.25B
By calculating how much B is less than A, the formula is (B - A) / B
Hence, (B - 1.25B) / A = -0.25B / 1.25B
The answer is - 0.2 (or - 20%)

Applying the same theory in the second question.
A = 1.6B
By calculating how much B is less than A, we use the same formula above
i.e. (B - 1.6B) / A
= - 0.6 B / 1.6 B
= - 0.375 (or - 37.5%)
That means B is 37.5% less than A.