In a book store, the sales of a book decreased by 80% from 2007 to 2008. If the sales in 2009 were the same as in 2007, would be the percentage increase in sales from 2008 to 2009?

Correct Answer: 80%
let, in 2007 was = 100 ,, 2008 ,, = 20 ,, 2009 ,, = 100 increase percentage = ( 100 - 20/20) = 400% (answer)