12) Find the sum, S7 for the geometric series {1 + 5 + 25 + - + 15625). [A] S, = 19531
[B] S, = 16536
[C] Sy = 15631
D] S, = 31256
[E] None of these

Understanding:

The sum of a geometric series is, , with a being the start point and r is the common ratio. We can also use the following formula to make life easier , a is your start point, r is the common ratio, and n is the number of terms, which in our case is S7.

Solution:

Our start point is 1, ,

The common ratio is 5, ,

And finally, the number of terms is 7, .

The answer is [A] 19531.

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step-by-step explanation: