The population of Smallville increased by 20% from 2000 to 2005 and it increased by 30% from 2005 to 2010. By what percent did the population of Smallville increase from 2000 to 2010?

Let P be the beginning poulation

At the end of 2005 the new poulation is (1.20)P

At the end of 2010, the population was (1.30) [ (1.20)P] = 1.56P

So....the poulation increased by (1.56 - 1) = .56 = 56% from 2000 to 2010