# Find `S_15` for 1 + 1.5 + 2.25 + 3.375 + ...

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The numbers 1, 1.5, 2.25, 3.375 form a geometric series with the first term 1 and the common ratio `1.5/1 = 1.5` .

The sum of the first n terms is `S_n = a*(r^n - 1)/(r - 1)`

The sum of the first 15 terms is `S_15 = 1*(1.5^15 - 1)/(0.5) ~~ 873.78`

**The value of `S_15` is approximately 873.78**