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If the sum of n consecutive positive integers is 42, which of these co

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New post 12 Apr 2019, 01:39
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[GMAT math practice question]

If the sum of n consecutive positive integers is 42, which of these could be the value of n?

A. 7
B. 8
C. 9
D. 10
E. 11

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Re: If the sum of n consecutive positive integers is 42, which of these co  [#permalink]

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New post 12 Apr 2019, 02:51
3+4+5+6+7+8+9 = 42

7 numbers - Option A
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If the sum of n consecutive positive integers is 42, which of these co  [#permalink]

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New post 12 Apr 2019, 02:55
MathRevolution wrote:
[GMAT math practice question]

If the sum of n consecutive positive integers is 42, which of these could be the value of n?

A. 7
B. 8
C. 9
D. 10
E. 11


sum of consective no n*(n+1)/2
given n^2+n= 84
n^2+n-84=0
not able to get the answer from this relation

other way
let first integer ; x ; so next x+1
lets try for n=7 ; 7x+21= 42
x= 3 ; sufficient
for other options we wont get integer value of x
IMO A .

I am not sure why answer is not coming from sum of consective no n*(n+1)/2 :|
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Re: If the sum of n consecutive positive integers is 42, which of these co  [#permalink]

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New post 12 Apr 2019, 03:04
Archit3110 wrote:
MathRevolution wrote:
[GMAT math practice question]

If the sum of n consecutive positive integers is 42, which of these could be the value of n?

A. 7
B. 8
C. 9
D. 10
E. 11


sum of consective no n*(n+1)/2
given n^2+n= 84
n^2+n-84=0
not able to get the answer from this relation

other way
let first integer ; x ; so next x+1
lets try for n=7 ; 7x+21= 42
x= 3 ; sufficient
for other options we wont get integer value of x
IMO A .

I am not sure why answer is not coming from sum of consecutive no n*(n+1)/2 :|


HI Archit3110

sum of consecutive no n*(n+1)/2 is for consecutive integers from n=1. But here we are not sure the consecutive integers are from n=1 or might be n=7 :-)

If you are adding Sum of consecutive integers of 100 then it would be 100*101/2 ==> 50*101 ==> 5050
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Re: If the sum of n consecutive positive integers is 42, which of these co  [#permalink]

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New post 12 Apr 2019, 03:09
NandishSS okay understood thanks..


NandishSS wrote:
Archit3110 wrote:
MathRevolution wrote:
[GMAT math practice question]

If the sum of n consecutive positive integers is 42, which of these could be the value of n?

A. 7
B. 8
C. 9
D. 10
E. 11


sum of consective no n*(n+1)/2
given n^2+n= 84
n^2+n-84=0
not able to get the answer from this relation

other way
let first integer ; x ; so next x+1
lets try for n=7 ; 7x+21= 42
x= 3 ; sufficient
for other options we wont get integer value of x
IMO A .

I am not sure why answer is not coming from sum of consecutive no n*(n+1)/2 :|


HI Archit3110

sum of consecutive no n*(n+1)/2 is for consecutive integers from n=1. But here we are not sure the consecutive integers are from n=1 or might be n=7 :-)

If you are adding Sum of consecutive integers of 100 then it would be 100*101/2 ==> 50*101 ==> 5050
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Re: If the sum of n consecutive positive integers is 42, which of these co  [#permalink]

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New post 12 Apr 2019, 04:11
[quote="Archit3110"]NandishSS okay understood thanks..
But trap would have been had question had both answer i.e with series starting from 1..
I feel it's ambiguous question ...

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If the sum of n consecutive positive integers is 42, which of these co  [#permalink]

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New post 12 Apr 2019, 08:38
MathRevolution wrote:
[GMAT math practice question]

If the sum of n consecutive positive integers is 42, which of these could be the value of n?

A. 7
B. 8
C. 9
D. 10
E. 11


mean=sum/n
if n is odd, mean 42/n must be integer
only 7 divides into 42
A
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Re: If the sum of n consecutive positive integers is 42, which of these co  [#permalink]

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New post 14 Apr 2019, 18:39
1
=>

Recall that the sum of terms of an arithmetic sequence is \({\frac{(a+l)}{2}}*n\) where a is the first term, \(l\) is the last term and \(n\) is the number of terms.

We are told that \({\frac{(a+l)}{2}}*n = 42\) or \(n(a+l) = 84.\)

Thus, \(n\) is a factor of \(84\).

\(7\) is the unique factor of \(84\) among the choices.

Therefore, the answer is A.
Answer: A
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Re: If the sum of n consecutive positive integers is 42, which of these co  [#permalink]

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New post 16 Apr 2019, 19:56
MathRevolution wrote:
[GMAT math practice question]

If the sum of n consecutive positive integers is 42, which of these could be the value of n?

A. 7
B. 8
C. 9
D. 10
E. 11


HI amanvermagmat, GMATGuruNY, pushpitkc Gladiator59 niks18

Any other method to solve these kind of problems?
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Re: If the sum of n consecutive positive integers is 42, which of these co   [#permalink] 16 Apr 2019, 19:56
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