1992 AJHSME Problems/Problem 25
Problem 25
One half of the water is poured out of a full container. Then one third of the remainder is poured out. Continue the process: one fourth of the remainder for the third pouring, one fifth of the remainder for the fourth pouring, etc. After how many pourings does exactly one tenth of the original water remain?
Solution
Model the amount left in the container as follows:
After the first pour remains, after the second remains, etc.
This becomes the product .
Note that the terms cancel out leaving .
Now all that remains is to count the number of terms, as the numerators form an arithmetic sequence with a common difference of 1 and endpoints (1,9), the number of pourings is .
See Also
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