Ivonne E.

asked • 03/18/15

a lily pad is growing in a pond and it doubles in size every day. after 30 days it covers the entire pond. on what day does it cover half pond

college algebra, solving exponentials and logs

Norman M.

This seems more like a riddle than algebra.  If on Day 30 it covers the whole pond, and it doubles in size each day, then on Day 29, it had to cover 1/2 the pond.


1 Expert Answer


Tan H. answered • 03/18/15

5.0 (286)

Breaking it down, step-by-step

Robert O.

Can you break that down, it's hard to wrap my head around this one?


Tan H.

Remember that the key word in this problem is "doubling in size" everyday. Supposed today (the 30th day) is the day the lily pad covered the entire pond. That means yesterday (the 29th day) the lily pad was half the size of the pond. In numbers: Pond size = 100 sq ft Lily Pad Growth ... Day 28 = 25 sq ft Day 29 = 50 sq ft (which is doubled the day before and is half the size of the pond) Day 30 = 100 sq ft (which is again doubled the day before and is now equal to the size of the pond) 30 days is arbitrary and any number could have been used. If a different problem says that it covers the pond on the 100th day, then the 99th day would be the day it covers half. If it covers it entirely on the 1345th day, then it would be the 1344th day that it covers half. Always the day before.


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