Engineering
Mathematics
Permutation and Combination Basic Definitions
Question

In a high school, a committee has to be formed from a group of 6 boys M1, M2, M3, M4, M5, M6 and 5 girls G1, G2, G3, G4, G5.

(i)         Let α1 be the total number of ways in which the committee can be formed such that the committee has 5 members, having exactly 3 boys and 2 girls.

(ii)         Let α2 be the total number of ways in which the committee can be formed such that the committee has at least 2 members, and having an equal number of boys and girls.

(iii)        Let α3 be the total number of ways in which the committee can be formed such that the committee has 5 members, at least 2 of them being girls.

(iv)        Let α4 be the total number of ways in which the committee can be formed such that the committee has 4 members, having at least 2 girls and such that both M1 and G1 are NOT in the committee together.

List - I List - II
(P)  The value of α1 is  (1)  136
(Q) The value of α2 is (2)  189
(R) The value of α3 is (3)  192
(S)  The value of α4 is (4)  200
  (5)  381
  (6)  461

The correct option is:

P → 4

Q → 6

R → 5

S → 2

P → 1

Q → 4

R → 2

S → 3

P → 4

Q → 6

R → 2

S → 1

P → 4

Q → 2

R → 3

S → 1

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Solution

(P)        α1 = 6C3 × 5C2 = 200

            (1B and 1G) + (2B and 2G) + (3B and 3G) + (4B and 4G) + (5B and 5G)

(Q)        α2 = 6C1 × 5C1 + 6C2 × 5C2 + 6C3 × 5C3 + 6C4 × 5C4 + 6C5 × 5C5

            = 30 + 150 + 200 + 75 + 6

            = 461

(R)       α3 = 11C5 – (6C4 × 5C1 + 6C5) = 381

(S)        α4 = 5C2 × 6C2 + 5C3 × 6C4 + 5C4 – (4C2 + 4C1 × 5C1)

            = 150 + 60 + 5 – (6 + 20) = 189.