Let's imagine that the question is about fractions. You want to decrease an about by 0.6 . Rather than 100 (which is for percentages), 1 is used instead. 1 - 0.6 = 0.4
To decrease an amount by 60%, the single multiplier you would use is 0.4
There is an easy way to check:
100 X 60% = 60
100 - 60 = 40
100 X 0.4 = 40
The fact that we got the same result using both the percentage and the multiplier moves that the latter is correct.
