You can put this solution on YOUR website! If a lily pad doubles in size everyday and on the 60th day it covers a lake...
On what day did it cover just half of the lake?
FULL ON 60 TH DAY
ONE DAY BEFORE ...59 TH DAY
IT IS HALF FULL.
59 TH DAY .SINCE IT DOUBLES EVERY DAY AND FILLS THE LAKE ON 60 TH.DAY