Question

To decrease an amount 70% what single multiplier would you use

Answer 1

Hello,

To reduce an amount by 70%, multiply it by 0.3.
Why 0.3? Because 0.3 = 1 - 70% = 1 - 0.7.

(Similarly, to reduce an amount by 20%, multiply it by 0.8.
Why 0.8? Because 0.8 = 1 - 20% = 1 - 0.2.)

Answer 2

If you want to decrease something by 70%, it is equivalent to saying you want to reduce it to (100-70) = 30% of its value. Since 30% is equal to 0.3, the single multiplier to use to decrease something's value by 70% is 0.3.
The general rule would be to subtract the % to decrease (like 70%) by from 100%, and convert to decimal form. This would give the single multiplier.