From 2008 to 2009, the sales of a book decreased by 80%. If the sales in 2010 were the same as in 2008, by what percent did it increase from 2009 to 2010 ?

Solution (By Examveda Team)

Decrease in sale = 80% from 2008 to 2009
Now, sales of 2010 are same as in 2008
:. Increase in sales
$$\eqalign{ & = \left[ {\frac{{100 \times {\text{a}}}}{{100 - {\text{a}}}}} \right]\% \cr & = \left[ {\frac{{100 \times 80}}{{100 - 80}}} \right]\% \,\,\,\left[ {{\text{a}} = 80\% } \right] \cr & = \frac{{8000}}{{20}}\% \cr & = 400\% \cr} $$