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28 Sep 2013, 11:31
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E
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Difficulty:
25%
(medium)
Question Stats:
73% (01:15) correct
27%
(01:08)
wrong
based on 312
sessions
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If the terms of a sequence are a1, a2, a3, . . . , an, what is the value of n ?
(1) The sum of the n terms is 1,048.
(2) The value of an is twice the value of a1
(1) The sum of the n terms is 1,048.
(2) The value of an is twice the value of a1
TirthankarP
Joined: 29 Apr 2013
Last visit: 10 Jan 2016
Posts: 80
Given Kudos: 53
Location: India
Concentration: General Management, Strategy
Schools: PGDM (GM) '15 (A)
GMAT Date: 11-06-2013
WE:Programming (Telecommunications)
28 Sep 2013, 12:14
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akshayb2
First of all we should note that there is noting mentioned about the sequence i.e. how each number in the sequence is related to its preceding or succeeding number.
Statement 1:
We can take any n numbers whose sum is 1048
1 + 1047 = 1048 ---> n = 2
1 + 2 + 1045 = 1048 ---> n = 3
INSUFFICIENT
Statement 2:
Lets plugin values for a1 and an.
an = 2*a1
an = 8, a1 = 4
But we don't know how a2 is related to a1 or how an-1 is related to an. So value of n can't be determined. Hence INSUFFICIENT
Combining Statement 1 and Statement 2:
Still not sufficient as we don't know how other numbers are related to each other on the sequence.
a1 + a2 + a3 + .... + an = 1048
=> a1 + a2 + a3 + .... + 2a1 = 1048
=> 3a1 + a2 + a3 + .... + (an-1) = 1048
We can take any values to satisfy this equation. Hence INSUFFICIENT
Answer E
29 Sep 2013, 12:30
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akshayb2
It's straight E.
n can be 2: 1,048/3 and 2*1,048/3.
n can be 3: 1,048/3, 0 and 2*1,048/3.
...
Hope it helps.
