The number of students increased from 640 to 768. What is the percent of change?

The pure numerical increase in this case would be 768 - 640 = 128 students. To find the percent increase this represents, we find first that the fraction of the original value 128 takes up is

128/640 = 1/5

As a decimal, 1/5 = 0.2, which we can then multiply by 100 to find our percent increase: 0.2 x 100 = 20%.

20% should be the correct answer

The pure numerical increase in this case would be 768 - 640 = 128 students. To find the percent increase this represents, we find first that the fraction of the original value 128 takes up is

128/640 = 1/5

As a decimal, 1/5 = 0.2, which we can then multiply by 100 to find our percent increase: 0.2 x 100 = 20%.