Jay has a pet grooming business. in 2010, he groomed 200 dogs. in 2011, he groomed 450 dogs. what was the percent increase in the number of dogs groomed

The way you figure out percent increase is you take the final number, divide it by the original number, and then subtract 1 from the result.  

Therefore, in this question, take the final number of 450, divide it by the original number, 200, and then subtract 1.

450 ÷ 200 - 1 =
2.25 - 1 =
1.25

1.25 is the same thing as 125%, so Jay increased the number of dogs he groomed by 125%.