By exercising regularly, Abby was able to improve her running right this year. Last year, Abby ran a mile in 12 minutes. This year she could run a mile in 10 minutes. By what percent did Abby decrease her running time?

She decreased her running time at a rate of 16.67%

Step-by-step explanation:

In this question, we are asked basically to calculate the percentage decrease in Abby's running time.

Mathematically, the percentage decrease equals: (new running time - old running time) / old running time * 100%

We input the values and proceed as follows:

Percentage decrease = (10-12) / 12 * 100

-2/12 * 100/1 = - 1/6 * 100 = - 16.67%

Since it's a decrease, we just simply say that her running time decrease by 16.67%