Mrs. Kemp began the school year with 20 students in her kindergarten class. She had 23 students at the end of the year. What was the percent of increase in the number of students from the beginning of the year to the end of the year?

First, we’re going to use this formula:

2nd number - 1st number
————————————— x 100%
1st number

If we plug in the numbers to this equation:

23-20
———- x 100%
20

And subtract 23 to 20, the answer to this equation is:

3
—- x 100% = 15%
20

In this case, the percent of increase is 15%.

The answer would be 13.5 minutes.