Find the sum to infinity of the geometric series 15 + 10 + 20/3 + ...

Answer and explanation

Correct answer: B. 45

  1. Step 1: The ratio is r = 2/3, and |r| < 1, so the series converges.
  2. Step 2: S = a/(1 - r) = 15/(1 - 2/3) = 45.
Answer
45.
Why not the others: '22.5' divides by r instead of 1 - r; '25' adds the first two terms only; '30' starts the sum at the second term.

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