Question

A student raises her grade average from a 75 to a 90. What was the percent of increase

Answer 1

This can be solved algebraically. Before we start, as context, to find a percentage you multiply by the percentage/100.

$75*x=90 \\ x= \frac{90}{75} \\ \\ \boxed{x=1.2}$

This tells us that 90 is 120% of 75. However, your question wants us to find the increase, therefore we don't need that 100.
Therefore, the increase is 20%.