Limiting Sums (1 Viewer)

[sasquatch]

Find the limiting sum of the series: 20 + 15 + 12 + ...

Considering the series, it is not geometric so how is it possible to find the limiting sum?

By using the common ratio (which this question does not have) between term 2 and term 1, r = 3/4, you can calculate the limiting sum to be 80 (which is what the answer has). But the ratio between terms 4 and terms 3, is 4/5. So yeah the question is wrong then right?

 

[SoulSearcher]

the question is flawed. the 3rd term should be 11.25 if the common ratio was really 3/4. so I guess you could say the question is wrong

 

[sasquatch]

I say wrong, because its not possible to find that series' limiting sum using the formula S = a / (1-r).

 

[Riviet]

I say wrong, because its not possible to find that series' limiting sum using the formula S = a / (1-r).

That's correct, r needs to be the same between any two consecutive terms in the series.