At the beginning of the summer matt swim 12 laps. at the end of the summer he could swim 15 laps. what is the percent increase in the number of laps mat and swim?

Percent change = (new number - old number)/(old number) * 100
A positive percent change is a percent increase.
A negative percent change is a percent decrease.

In this problem, we have:
The new number is 15 laps.
The old number is 12 laps.

percent change = (15 - 12)/(12) * 100

percent change = 3/12 * 100

percent change = 25

Since the percent change is positive, +25, it is a percent increase.

The percent increase is 25%