Multiple choice

A and B toss a coin alternatively, the first to show a head being the winner. If A starts the game, the chance of his winning is?

  1. $5/8$
  2. $1/2$
  3. $1/3$
  4. $2/3$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

A wins on 1st toss (1/2), 3rd (1/2 * 1/2 * 1/2 = 1/8), 5th (1/2^5 = 1/32), etc. This is a geometric series with a = 1/2 and r = 1/4. Sum = a / (1 - r) = (1/2) / (1 - 1/4) = (1/2) / (3/4) = 2/3.

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