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Consider the sets S1 = (1) S2 = (2,3) S3 = (4,5,6) S4 = [#permalink]
 03 Oct 2004, 09:43
Consider the sets
S1 = (1)
S2 = (2,3)
S3 = (4,5,6)
S4 = (7,8,9,10)
What is the sum of terms in the set S100 ?
Edited :
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Franky
http://franky4gmat.blogspot.com
Last edited by myfrankenstein on 03 Oct 2004, 12:59, edited 1 time in total.
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Director
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Is it 500050.
The approach was..
S1 = (1)
S2 = (2,3)
S3 = (4,5,6)
S4 = (7,8,9,10)
S5 = (11,12,13,14,15)
S6 = (16,17,18,19,20,21)
S7 = (22,23,24,25,26,27,28)
S8 = (29,.....,36)
S9 = (37....)
..
..
S99 = (4852,...) Note: [99*49 +1 = 4852]
S100 = (4951,...) Note: 4852+99 = 4951
Using AP, Sum = (100/2)(2*4951 + 99*1)
= 500050
Last edited by venksune on 03 Oct 2004, 19:01, edited 1 time in total.
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Director
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venksune, I was thinking the same, but did you see that he repeated 3 in S2 and S3.
Your approach would be correct if the wuestion was:
S1 = (0)
S2 = (1,2)
S3 = (3,4,5)
S4 = (6,7,8,9) ...
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Director
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Oops. I did not. I copied his 4 sets blindly when posting. When I did the problem offline, I took the set as you did. I think I will sleep now..
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Manager
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I made an edit. Apologies.
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Franky
http://franky4gmat.blogspot.com
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Director
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I have edited my post too.
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Director
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Sum of Sn terms = n(n^2+1)/2
S100 = 500050
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