Question

Calculate the sum of the infinite series 72 + 60 + 50 + 125/3 + ...

489
432
360
307

Can someone please help me with this one? I can never solve these on my own:(

Answer 1

if it is geometric, r=60/72=10/12=5/6
adn then 5/6(60=50
and then 40(5/6)=200/6=100/3, so that is not a geometric series. Did your teacher make an error? Lets test if she meant it to be a geometric series, r=5/6

sum=72/(1-5/6)=72*6=amazing, the answer is there.

So I bet your teacher meant 100/3 as the fourth term.

Answer 2

Oh ok, thank you so much.

Answer 3

Nah. Where did you get the 40? 50 * 5/6 = 250/6 = 125/3

so, you have a genuine GP, with
a = 72
r = 5/6

So, S = 72/(1 - 5/6) = 72*6 = 432