PrepRung
Sign inSign up free

NDA 2018 Maths · Mathematics · Statistics · easy

A box has 3 white and 5 black balls. Two balls are drawn one after another without replacement. The probability that they are of different colours is

Single correct option

A box has 3 white and 5 black balls. Two balls are drawn one after another without replacement. The probability that they are of different colours is
  1. A. 1564\frac{15}{64}
  2. B. 1556\frac{15}{56}
  3. C. 1528\frac{15}{28}
  4. D. 38\frac{3}{8}
Show answer and solution

Answer: (C) 1528\frac{15}{28}

The order can be white-black or black-white: 38⋅57+58⋅37=3056=1528\frac38\cdot\frac57+\frac58\cdot\frac37=\frac{30}{56}=\frac{15}{28}. The value 1556\frac{15}{56} counts only one order, and 1564\frac{15}{64} treats the draws as with replacement.
Report a mistake

Original question written in the NDA 2018 Maths pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake