In the middle of a round pool lies a beautiful water lilly.The water lilly doubles in size every day.After exactly 20 days the complete pool will be covered by the water lilly.After how many days will half of the pool will be covered by the water lilly ?

• 19 days
  
  Method I
  here water lily doubles its size every day, so if after 20 days the complete pool be covered, so at 19th day half of the pool will be covered.
  
  Method II
  acc to the question, number of water lily at nth day is given by 2^(n-1;so after 20 days number of water lily is 2^(20-1)=2^19=524288; half of this is 262144 which is 2^18=2^(19-1)
  i.e. n=19
• 10 years agoHelpfull: Yes(5) No(0)
• After 10 days bcos the entire pool is covered by lilly in 20 days
• 10 years agoHelpfull: Yes(0) No(3)