Question 517564: At noon, 1/4 of the birds perched on fence flew away,but 1 came back. At 1pm,1/2 of the remaining birds flew away,but 2 came back. Finnally, at 2pm,1/2 of the remaining birds flew off, and 5 birds remained. How many birds were originally perched on the fence before they started leaving at noon?
Answer by solver91311(24713)   (Show Source):
You can put this solution on YOUR website!
Work from the end of the problem back to the beginning.
5 left at the end, but this is half of what was there at 2 pm, so at 2 pm there were 10. But this is 2 more than half of what was there at 1 pm, 8 times 2 is 16. But this is 1 more than 3/4 of what was there at noon 15 is 3/4 of 20.
John
My calculator said it, I believe it, that settles it
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