akshayb2 wrote:

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

plz explain

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
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