Set A is made up of every 1/n
, where n is
a positive integer and 100 ≤ n ≤ 150.
If S is the sum of all the elements in A,
then:
(A) S < 1/3
(B)1/3 < S < 1/2
(C) 1/2 < S < 1
(D) 1 < S < 1 1/2
(E) 1 1/2 < S < 2
pls tell me how to solve this.
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- gmatboost
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If every number in the set was as big as the biggest element (1/100) the sum would be:Set A is made up of every 1/n, where n is a positive integer and 100 ≤ n ≤ 150.
If S is the sum of all the elements in A, then:
51*(1/100) = 51/100 = about 1/2
If every number in the set was as small as the smallest element (1/150) the sum would be:
51*(1/150) = 51/150 = about 1/3
The actual sum lies somewhere in between, since the terms start out at 1/100 and slowly make their way to 1/150. So, the sum is somewhere in between 1/2 and 1/3.
Greg Michnikov, Founder of GMAT Boost
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- gmatboost
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Yes:
There are 51 numbers in the range 100 ≤ n ≤ 150.Set A is made up of every 1/n, where n is a positive integer and 100 ≤ n ≤ 150.
Greg Michnikov, Founder of GMAT Boost
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- gmatboost
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It definitely had nothing to do with anything related to a harmonic series. That kind of stuff is NOT on the GMAT.
It had to do with just counting the number of terms, from the biggest one (1/100) to the smallest one (1/150). There are 51 terms because there are 51 numbers from 100 to 150, inclusive.
It had to do with just counting the number of terms, from the biggest one (1/100) to the smallest one (1/150). There are 51 terms because there are 51 numbers from 100 to 150, inclusive.
Greg Michnikov, Founder of GMAT Boost
GMAT Boost offers 250+ challenging GMAT Math practice questions, each with a thorough video explanation, and 100+ GMAT Math video tips, each 90 seconds or less.
It's a total of 20+ hours of expert instruction for an introductory price of just $10.
View sample questions and tips without signing up, or sign up now for full access.
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GMAT Boost offers 250+ challenging GMAT Math practice questions, each with a thorough video explanation, and 100+ GMAT Math video tips, each 90 seconds or less.
It's a total of 20+ hours of expert instruction for an introductory price of just $10.
View sample questions and tips without signing up, or sign up now for full access.
Also, check out the most useful GMAT Math blog on the internet here.