Multiple choice general knowledge math & puzzles

Sum of the series (1+2x+3x2+............ to infinity) when x = 0.5

  1. 1

  2. 2

  3. 3

  4. 4

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The series is an arithmetico-geometric progression. The sum of 1 + 2x + 3x^2 + ... is given by the formula 1/(1-x)^2 for |x| < 1. Substituting x = 0.5, we get 1/(1-0.5)^2 = 1/(0.5)^2 = 1/0.25 = 4.