What is the sum of the first five terms of a geometric series with a1 = 10 and r = 1/5?

Express your answer as an improper fraction in lowest terms without using spaces.

Question

What is the sum of the first five terms of a geometric series with a1 = 10 and r = 1/5? 

Express your answer as an improper fraction in lowest terms without using spaces.

anonymous · Answer

Anyone wanna help me w the rest of this quiz?

kirbykirby · Answer

$$\Large \sum_{x=0}^nar^x=a\frac{1-r^{n+1}}{1-r} $$

anonymous · Answer

I get what to put for, but what do I put for n?

kirbykirby · Answer

Since you're interested in the first 5 terms.. 
you get
$a+ar+ar^2+ar^3+ar^4$, so since it goes until $ar^4$, n = 4

anonymous · Answer

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So far so good?