Question

mary decreased her time in the mile walk from 30 minutes to 24 minutes. What was the percent of decrease?

Answer 1

(24/30)*100 = 80%

Therefore she decreased from 100% to 80%, which is about 20% decrease.
Thus, the answer is 20%



Another way to do this is.

$\frac{(Original value - current value)}{Original value} * 100% = percentage of change in value$


Which in this case is 
$\frac{30-24}{30} * 100% = 20%$