Greg weighed 140 pounds. on his diet he lost 15 pounds. what was the percent of decrease in greg’s weight?

Well first you want to find out how much he weighed after his diet. 
140-15= 125
Next you want to take that and divide it by 140
125/140= 0.8928571
To make it a percent multiply by 100
0.8928571*100= 89.28571
Subtract from 100
100-89.28571= 10.71249
He had a 10.71249% decrease in weight