OA: C
Please explain..
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Geva@EconomistGMAT
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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.
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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irock
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thank you Geva 
now the problem looks so simple when you know how to approach!!
now the problem looks so simple when you know how to approach!!
We are what we repeatedly do. Excellence, therefore, is not an act but a habit - Aristotle.
