We need to find the approximate value of 1/45+1/46+1/47+1/48+1/49+1/50+1/51+1/52+1/53+1/54. Now, the sum of these 10 terms will be very close to 10 times 1/50, which is 0.02*10=0.2.

Answer: B.
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I got 0.2 too (B). Please help. Here is my approach
(1/45) + (1/46) + .....+(1/54) = (45-44)/45 +(46-45)/46 +.....+(54-53)/54
= 10 -(44/45 + 45/46 + ...53/54). Each term in the bracket is > 0.977, and there are ten of them. Then their sum is roughly 9.8
10-9.8 = 0.2. But is this doable in 2 mn under stress and heat?
Brother Karamazov



Brother Karamazov

Such questions do not test your calculations. (In fact most of GMAT questions) They test your logic and how easily can you simplify a problem.
That is why an approximate result is asked and not the absolute value.

Out of the given numbers, from 45 to 54, carrying out calculations with 50 would be easiest.

Hene instead of 1/45 + 1/46 + ... 1/50 + ... + 1/54,
We can increase some terms and decrease some terms by changing the numbers with 50

Hence we have a sequence = 1/50 + 1/50 + ... + 1/50 (Total 20 terms)
= 10/50 = 1/5 = 0.2 approximately
Option B

We need to determine the approximate value of the sum of the reciprocals from 45 to 54 inclusive; thus, we need the approximate value of the following:

1/45 + 1/46 + 1/47 + 1/48 + 1/49 + 1/50 + 1/51 + 1/52 + 1/53 + 1/54

Rather than adding each of these numbers (which would be incredibly time-consuming), let’s strategically select one of the fractions in our list and add it to itself 10 times. That sum will give us an approximate value for S.

Scanning the list, we see the best number to add to itself 10 times is 1/50. However, instead of actually adding 1/50 ten times, we will simply multiply it by 10:

1/50 x 10 = 10/50 = 1/5 = 0.2

Thus, we see that S is approximately 0.2.

Answer: B
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