Question

A box contains two white balls, three black balls and four red balls. In how many ways can three balls be drawn from the box if at least one black ball is to be included in the draw

• A. 64
• B. 45
• C. 46
• D. None of these

Answer 1

Answer: (A)

64

Answer 2

A selection of 3 balls so as to include at least one black ball, can be made in the following 3 mutually exclusive ways

i) 1 black ball and 2 others = ³C₁ x ⁶C₂ = 3 x 15 = 45

ii) 2 black balls and one other = ³C₂ x ⁶C₁ = 3 x 6 = 18

iii) 3 black balls and no other = ³C₃ = 1

∴Total numbers of ways = 45 + 18 + 1 = 64.