Question

Find the sum of first 10 terms of the G.P 3, 6, 12, 24___

Answer 1

a = 3

r = 2

Sum of n terms $S_n$ = $\frac{a(r^n-1)}{r-1}$

$S_{10}$ = $\frac{a(r^{10}-1)}{r-1}$

= $\frac{3(2^{10}-1)}{2-1}$

= (1024 - 1) × 3

$=1023\times 3$

= 3069