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 Question from Rattanjeet, a student: Find the sum of 1(1/2) + 2(1/4) + 3(1/6) + 4(1/6)(3/4) + 5(1/6)(3/4)2 + 6(1/6)(3/4)3+ ... where 1/6 + (1/6)(3/4) + (1/6)(3/4)2 + ... constitutes a geometric series.

Hi Rattanjeet,

Look at the infinite series $\large \frac{1}{1 - x} = 1 + x + x^2 + x^3 \cdots$ and its derivative for a clue.

Penny

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