Question

The population of lilies in a pond doubles every day. If it takes 30 days for the lilies to cover the entire pond, how much time does it take them to cover half the pond?

Answer 1

the number of water lilies doubles every day and the pond is covered

entirely in 30 days, we deduce that after 29 days, the progeny of a single water lily

covers half of the surface of the pond

we can note the number of water lilies

descendant of a water lily as 2n, where n is the number of days since the beginning.

Now, if we start with two water lilies, the total number of water lilies after t days will be

obtained by 2t + 2t = 2(2t) = 2t+1. If we want the final quantity generated by a water lily

is the same as that generated by two water lilies, then 2n = 2t+1, so t +1 =n

If n is 30 days, then t is 29 days

Explanation: