Sum of Reciprocals

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by GMATGuruNY » Mon Oct 12, 2015 6:37 am
If K is the sum of reciprocals of the consecutive integers from 43 to 48, inclusive, then K is closest in value to which of the following?

A. 1/12
B. 1/10
C. 1/8
D. 1/6
E. 1/4
K = 1/43 + 1/44 + 1/45 + 1/46 + 1/47 + 1/48.

Determine the RANGE of the sum.

The smallest fraction = 1/48.
If all of the 6 fractions were 1/48, the result would be the following sum:
6(1/48) = 1/8.
Since all but one of the fractions are actually GREATER THAN 1/48, the value of K must be GREATER THAN 1/8.

The greatest fraction = 1/43.
If all of the 6 fractions were 1/42, the result would be the following sum:
6(1/42) = 1/7.
Since all of the fractions are actually LESS THAN 1/42, the value of K must be LESS THAN 1/7.

Thus:
1/8 < K < 1/7.

Answer choices A and B are BELOW this range.
Answer choices D and E are ABOVE this range.

The correct answer is C.
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by Brent@GMATPrepNow » Mon Oct 12, 2015 8:56 am
Here's a similar question to practice Mitch's technique: https://www.beatthegmat.com/13th-edition ... 79692.html

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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