What is a percentage?
A percentage is a ratio, or a number expressed in the form of a fraction of 100. Percentages are often used to express a part of a total.
First, we need to figure out the amount the price increased.
50 - 40 = 10
The price of the yearbook this year increased $10.
Now, taking 10, we need to figure out what percent of 40 is 10.
10 ÷ 40 = 0.25
10 is %25 of 40.
Therefore, the price increase from last year to this year is %25.