Data Sufficiency

Q. If the terms of a sequence are t1, t2, t3......tn what is the value of n?

1. The sum of n terms is 3124

2. The average (arithmatic mean) of n terms is 4

Q. If the terms of a sequence are t1, t2, t3......tn what is the value of n?

1. The sum of n terms is 3124
3124=t1 + t2 + t3 +..... +tn
We can't find n, too many unknowns (right word?)

2. The average (arithmatic mean) of n terms is 4
4=(t1 + t2 + t3 +..... +tn)/n
We can't find n, too many unknowns.

1 and 2
4=3124/n
n=781

C for me

yup,both statements enough.

C.

The OA is C.

If the sequence is AP, then ans is C..
but the sequence can be AP or GP or HP...

so why did we assume the sequence to be AP..

Can somebody explain?

Operation780 wrote:The OA is C.

If the sequence is AP, then ans is C..
but the sequence can be AP or GP or HP...

so why did we assume the sequence to be AP..

Can somebody explain?

Think about the average of anything;

Average = (sum of terms/# of terms)

The question asks us what the # of terms is.

1) Average = (3124)/# of terms - we don't know the average or # of terms so we cant solve for # of terms. Insufficient.

2) 4 = (Sum of terms/# of terms) - We don't know the sum of terms or the number of terms so we cant solve for the number of terms. Insufficient.

1 and 2 together tells us;

4 = 3124/# of terms - You could calculate this out and solve for the number of terms, but simply knowing this allows us to conclude that C is the answer.

Hope this helps.

Thanks,

Jared