P→4; Q→6; R→2; S→1
P→4; Q→6; R→5; S→2
P→4; Q→2; R→3; S→1
P→1; Q→4; R→2; S→3
(1) α1 = (6C3)(5C2) = 20 × 10 = 200 So P→4
(2) α2 = (6C1)(5C1) + (6C2)(5C2) + (6C3)(5C3) + (6C4)(5C4) + (6C5)(5C5) = 30 + 150 + 200 + 75 + 6 = 461 So Q→6
(3) α3 = (5C2)(6C3) + (5C3)(6C2) + (5C4)(6C1) + (5C5)(6C0) = 200 + 150 + 30 + 1 = 381 So R→5
(4) α4 = (5C2)(6C2) - (4C1)(5C1) + (5C3)(6C1) - (4C2)(5C0) + (5C4) = 150 - 20 + 100 - 6 + 5 = 229
(5C2)(4C2) = 60
(5C3)(4C1) = 40
(5C2)(4C2) + (5C3)(4C1) + 5C4 = 60 + 40 + 5 = 105
Total ways = 105
Total ways to select 4 members = 11C4 = 330
Total number of ways to select 4 members with at least 2 girls = 11C4- (6C4)(5C0) - (6C3)(5C1) - (6C2)(5C2) = 330 - 15 - 100 -150 = 65
(5C2)(4C2) = 60
(5C3)(4C1) = 40
α4 = (5C2)(4C2) + (5C3)(4C1) + 5C4 = 60 + 40 + 5 = 105
The number of ways to choose 4 members such that at least 2 are girls = (5C2)(6C2) + (5C3)(6C1) + (5C4)(6C0) = 150 + 100 + 5 = 255
Ways to choose M1 and G1 together = (4C1)(4C1) = 16
Then 255 - 16 = 239
α4 = 189
So S→2