AMC / AIME · Geometric Sequences · Hard

Geometric Sequences: Find the first ten-term sum of math.

Common ratios.

Try the problem

Find the first ten-term sum of 5,10,20,…5,10,20,\ldots.

Hint and answer

Concept to use

Infinite $|r|<1$.

Hint

Use ratios for terms and the finite or infinite geometric-sum formula.

Answer

5115

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