Bunuel wrote:
Notice that the total number of lilies is not 1+2+2^2+2^3..2^30, it's 2^30.
Initially = 1;
After 2 days = 2, not 1+2;
After 4 days = 2^2 = 4, not 1+2+4.
...
After 60 days = 2^30, not 1+2+2^2+2^3+...+2^30.
Similarly, if initially there are 2 lilies, then the total number would be 2*2^x.
So, we'd have that 2^30 = 2*2^x --> x = 29.
Hope it helps.
The number of water lilies on a certain lake doubles every two days. If there is exactly one water lily on the lake, it takes 60 days for the lake to be fully covered with water lilies. In how many days will the lake be fully covered with lilies, if initially there were two water lilies on it?
(A) 15
(B) 28
(C) 30
(D) 58
(E) 59
hey Bunuel,
i have a doubt in the first part of the problem it is given that if there is one lily it will take 60 days and number of water lillies double every 2 days.
so, it is in GP and the terms will be a, ar, ar^2, ar^3 etc. here it is 1,2,4,8....
we need to find the 30th term which will be ar^n-1 gives us ar^29 that leads to 1(2^29) but you got it as 2^30
what is wrong with what i did?