What is the probability that boys and girls sit alternatively?

Consider the following for the next five (05) items that follow: Three boys P, Q, R and three girls S, T, U are to be arranged in a row for a group photograph.

  1. A. \frac{4}{5}
  2. B. \frac{1}{10}
  3. C. \frac{5}{6}
  4. D. \frac{1}{7}

Correct Answer: B. \frac{1}{10}

Explanation

The alternate seating can follow two patterns: BGBGBG or GBGBGB. For each pattern, the 3 boys can be arranged in 3! = 6 ways and the 3 girls in 3! = 6 ways. Number of favorable outcomes = 2 \times 6 \times 6 = 72. The probability is \frac{72}{720} = \frac{1}{10}.

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