Question

The 4th and 7th terms of GP are 16 and 2 respectively.Find; a)the first term b)the common ratio c)the sum of the first 3 terms.

Answer 1

r^3 = 2/16 = 1/8

r = 1/2
a(1/2)^3 = 16, so a = 128
S3 = 128 (1 - 1/8)/(1 - 1/2) = 224

check: 128+64+32 = 224