Question

If the ratio of sum of n terms of two AP’s is

(3n + 1) : (2n + 3) then the ratio of their 11^th term-

• A. 45 : 64
• B. 3 : 4
• C. 64 : 45
• D. 4 : 3

Answer 1

Answer: (C)

64 : 45

Answer 2

$\frac { \mathrm { S } _ { \mathrm { n } } } { \mathrm { S } _ { \mathrm { n } } ^ { \prime } } = \frac { 3 \mathrm { n } + 1 } { 2 \mathrm { n } + 3 }$

For ratio of 11^th term,

Put n = 2 × 11–1 = 21

So, $\frac { \mathrm { T } _ { 11 } } { \mathrm {~T} ^ { \prime } { } _ { 11 } } = \frac { 3 ( 21 ) + 1 } { 2 ( 21 ) + 3 } = \frac { 64 } { 45 }$