Question

A delegation of five students is to be formed from a group of 10 students. If three particular students want to remain together whereas two particular students do not want to remain together then the number of selections, is –

• A. 10
• B. 20
• C. 30
• D. None of these

Answer 1

Answer: (B)

20

Answer 2

A, B, C want to remain together. D, E do not want to remain together.

In Out Number of Selections

A, B, C, D E ⁵C₁ = 5

A, B, C, E D ⁵C₁ = 5

D A, B, C, E ⁵C₄ = 5

E A, B, C, D ⁵C₄ = 5

Required number of selections is

⁵C₁ + ⁵C₁ + ⁵C₄ + ⁵C₄ = 20