Answer:
3, …., 243 (m A.M)
d = (b-a)/(n+1)
= (243-3)/(m+1)
= 240/(m+1)
4th AM = 3+4d
= 3+4(240/m+1)
3, …, 243 (3G.M)
243 = 3r4
r = 3
2nd G.M = ar2 = 27
Given that 4th A.M. is equal to 2nd G.M.
3+(960/m+1) = 27
= 960/m+1 = 24
⇒ m = 39
the answer is 39
