Answer:
Correct option: D
Explanation:
First we need to find the rate of the series, and we can do that subtracting one term by the term before:
Second term minus first: 13/10 - 1/2 = 13/10 - 5/10 = 8/10 = 4/5
Third term minus second: 21/10 - 13/10 = 8/10 = 4/5
So the series increases by 4/5 for every term, and the first term is 1/2
We also need to find the number of terms of this series.
The last term is 93/10, so we have that:
1/2 + (4/5)*k = 93/10
(4/5)k = 88/10
k = 11
The index of the summatory should go from 0 to 11.
So the correct option is D