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by irock » Sun Jul 10, 2011 6:54 am
OA: C

Please explain..
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by Geva@EconomistGMAT » Sun Jul 10, 2011 8:22 am
Try an entry point or two: How can you reach a sum of 350 with only 7s, or only 77s?

If you had 50 terms, each equaling 7 their sum would be 350. So if we had an answer choice saying "50", that would've been correct. The problem is, we don't - all the ACs are smaller than 50. Apparently some of the "7s" convert to "77", to reach the same sum with fewer terms.

For here, it's trial and error. Let's introduce 1 term of 77, which would enable us to discard 11 "7s" and still reach the same sum of 350. How many terms do we have now? Careful: we're down 11 from our original 50 (to 39), but we've added a single "77", to reach a grand total of 39+1=40 terms.
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by irock » Sun Jul 10, 2011 8:34 am
thank you Geva :)
now the problem looks so simple when you know how to approach!! :)
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