SOLUTION: A tortoise travelled 4096 m in week one. Each week, it travelled half as far as the previous week. In what week will the tortoise travel 4 m? I know what the answer is (11 week) be

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Question 696832: A tortoise travelled 4096 m in week one. Each week, it travelled half as far as the previous week. In what week will the tortoise travel 4 m? I know what the answer is (11 week) because I used a caculator but I want to know what the "formula" or equation is. Something Like 2nx+1=y, Please help!
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
A tortoise travelled 4096 m in week one. Each week, it travelled half as far as the previous week. In what week will the tortoise travel 4 m?
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d+=+4096%2A%281%2F2%29%5E%28w-1%29 w = # of week from 1 to ....
or
d+=+8192%2A%281%2F2%29%5Ew w = # of week from 1 to ....
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4+=+8192%2A%281%2F2%29%5Ew
%281%2F2%29%5Ew+=+1%2F2048
w*log(1/2) = log(1/2048)
w = log(1/2048)/log(1/2)
w = 11