By what percent will the product of two numbers decrease if one of them is decreased by 25% and the other one is decreased by 50%?

Well, let's say the numbers are "a" and "b"

so a * b = ab

ok... now, if we reduce "a" by 25%, that means the new size is just 75% of the old one, how much is 75% of a? well, (75/100) * a, or 0.75a

now let's reduce "b" by 50%, that means the new size is 50% or half,  how much is 50% of b? well (50/100)*b, or 0.5b



now, the new size of "ab" is just 0.375ab... well, let's revert the decimal format by simply multiplying by 100

0.375 * 100, is 37.5%

the new size of "ab" is just 37.5% of the original "ab"

it decreased by 100 - 37.5 or 62.5%