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.
 
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03/18/15

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Kyle L. answered • 08/18/25

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Hello, thank you for taking the time to post your question!


You can just think through this one logically! If it’s doubling in size every day that means that the day before it covered the entire pond it would have covered half of the pond. So it would be the 29th day where it covered half of the pond.


I hope that helps you get moving in a better direction on this type of question! Feel free to reach out if you have any additional questions beyond that :)

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Tan H. answered • 03/18/15

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Breaking it down, step-by-step

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If the lily pad covers the entire pond on the 30th day, and it is doubling in size everyday, then the day before (the 29th day) it covered half of the pond. 
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Robert O.

Can you break that down, it's hard to wrap my head around this one?
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11/09/20

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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11/10/20

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