A number is decreased by 15% and then increased by 12.5%. The number so obtained is 21 less than the original number. What was the original number?

480

             Actual No.   :    New No.      

-15%           20        :       17

+12.5%         8       :       9

                   —————————

Total Effect   160      :     153    ⇒    7 (decrease)

         7 Unit = 21

 Original no. is = 160 Units = 160 × 3 = 480