The sum of first three terms of a GP and the sum of first six terms of GP is in ratio 125 152 Find t...........

Quantitative Aptitude (CDS) Arithmetic progression

The sum of first three terms of a GP and the sum of first six terms of GP is in ratio 125:152.Find the common ratio of GP?

3/4

4/5

3/5

none of these

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Explanation:

sum of first three term of G.P is =a(r^3-1)/r-1
sum of first six term of G.P is =a(r^6-1)/r-1
ratio of both sum is 125:152
125/152 =r^3 -1 / r^6 -1
=r^3 -1 / (r^3)^2 -1
=r^3 -1 / (r^3 -1)(r^3 +1)
=1/ r^3 +1
=r^3 +1 =152 /125
r^3 =(152 -125 )/125
r^3 =27/125
r =3/5