How to find the percent increase in a word problem?

Question

At a cell phone store the number of phones sold in August increased by 20% over sales in July. Sales of phones increased in September by another 10% over sales in August. What was the overall percent increase in the number of phones sold during the two months.

Answer 1

to make this easy to understand let the sales in July be 100

20% of 100=20

August sales were 100+20=120

10% of 120=12

September sales were 120+12=132

100 to 132 is (132-100)/100=32/100=32% increase

 

or,...

x+0.2x=1.2x

0.1*1.2x=0.12x

1.2x+0.12x=1.32x which implies a 0.32 or 32% increase