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test 13 #20

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Source: — Data Sufficiency |
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by sanju438 » Wed Oct 01, 2008 1:07 pm
S = n(n+1)/2
(1) S < 20. Insufficient. n can be 1, 2 etc
(2) S^2 > 220. Insufficient . n can be 6, 7, etc

Taking (1) and (2) together, only n = 5 is possible. Sufficient
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by raju232007 » Fri Oct 03, 2008 9:26 am
But it is given that S is the sum of first n natural numbers....so as per the first statement S<20
This is possible only when n=5 (i.e 1+2+3+4+5)
if n=6 S becomes 21...so th only solution is n=5

if u consider the second statement S can be anything(i.e S>14.5)
so n can be 5,6,78 etc...

So I think the ans should be A..Correct me if i am wrong..
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by Morgoth » Fri Oct 03, 2008 9:35 am
raju232007 wrote:But it is given that S is the sum of first n natural numbers....so as per the first statement S<20
This is possible only when n=5 (i.e 1+2+3+4+5)
if n=6 S becomes 21...so th only solution is n=5

if u consider the second statement S can be anything(i.e S>14.5)
so n can be 5,6,78 etc...

So I think the ans should be A..Correct me if i am wrong..
First statement is insufficient.

if n=2
S = 2+1 = 3 <20

if n=3
S=1+2+3=6 <20

if n=4
S=1+2+3+4=10 <20

if n=5
S=1+2+3+4+5=15 <20

therefore, 0 < n < 6. Insufficient.

Hope this helps.
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by raju232007 » Fri Oct 03, 2008 9:45 am
Thanks for your explanation...the ans is C..
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