The first thirdd and ninth terms of am AP are the first three terms of a GP. If the seventh term of AP is 14, calculate (a) the 20th term (b) the sum of the first twelve terms of the GP

1 answer

just use what you know about AP's and GP's:

(a+2d)/a = (a+8d)/(a+2d)
a+6d = 14

AP: 2,4,6,8,...
GP: 2,6,18,...

Now you can easily find terms and sums.