Question

How many terms of the gp 1+4+16+64+.... Will sum up to 5461?

Answer 1

Answer:

the answer is no. of terms = 7.

here , a = 1 ; r = 4 .......(r > 1)

therefore,

Sn = a( r^n - 1 )/r -1=5461

= 1(4^n - 1)/4-1 = 5461

= 4^n - 1 = 16383

= 4^n = 16384

=4^n = 4^7

on comparing both sides,

n = 7