Question

answer this question...

Answer 1

Sn/S"n = (7n -5)/(5n +17)
arrange in standard form .

= n/2{ 2.1 +(n -1)7}/n/2{2.11 + ( n -1)5 }

now, you can see that
for Sn
a = 1 and d = 7

for S"n
a = 11 and d = 5

now,

Tn/T"n = { 1 + ( n -1)7}/{11 + ( n -1)5 }

= ( 7n -6)/( 5n + 6)

a/c to question,
Tn = T"n

7n -6 = 5n + 6

2n = 12

n = 6

hence option (b) is correct answer