Hard one

[Stormgal]

In the infinite sequence A, ,
where x is a positive integer constant. For what value of n is the ratio
of to equal to ?

(A) 8
(B) 7
(C) 6
(D) 5
(E) 4

source: Manhattan GMAT

[mba05]

is it B ? n = 7

[udaygrover]

I most humbly and respectfully would go for B too... whats the answer..!

[Seriph]

I get answer of 7, or B, too. How would you approach this problem in general other than plugging in the answers after expanding the denominator?

[Sargataur]

any more thoughts on this one

[kalipegasus]

The method I followed was to reduce the Q to (x^6/ x ) * ( Y/Y)
the eqn An= (x ^ n -1)(1+ x + x^2 + x^3 +.... ) ----------------------------(1)

and the eqn x(1+x(1+x(1+x...))))
which i call Z can be reduced to x( 1+x+x^2+x^3 ..) --------(2)

from (1) and (2) we get An / Z = x^(n-1) / x
therefore for getting answer x^5 (n-1) = 6
therefore n=7

answer: B

[HJAIN]

Its B.

[vinesh]

b for me too

[Stormgal]

Originally Posted by Sargataur

any more thoughts on this one

Sargataur, is this the type of question one would encounter on the GMAT?

[ashok_sharma]

[quote=Stormgal]In the infinite sequence A, ,
where x is a positive integer constant. For what value of n is the ratio
of to equal to ?

(A) 8
(B) 7
(C) 6
(D) 5
(E) 4

the answer is B