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Bunuel
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Great observation.

The answer choices analysis is the quickest route to the answer.

ktzsikka
Without solving, we observe that S =sum of 7 positive numbers.
Hence, S will always be greater than any of those individual number.
Thus 1 is out and 2 & 3are correct.
Option d is correct.
Q. E. D.

Posted from my mobile device
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This kind of questions can be solved in 30 seconds
The correct answer is D here.
Here is why:
S=1/10 + 1/20 + ... + 1/70

I) S < 1/10 It can never be less than 1/10 because we are adding values to 1/10, hence it is out.
II) S>1/70. It is definitely true because the first value (1/10) is greater than 1/70. Hence the sum of 1/10 + 1/20 + ... +1/70 will be definitely greater than 1/70
II) S>1/40. The same as in II

Thus, the correct answer is II and III (D)
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Let's find out the possible MAXIMUM & MINIMUM Values for S.

S would be MAXIMUM if all values would equal to 1/10:

Thus, S(Max) = 7/10 = 0.7

S would be MAXIMUM if all values would equal to 1/70:

Thus, S(Min) = 7/70 = 0.1

0.1< S<0.7

which means options II & III are always true in this case (D)
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