JEE Challenger
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Ways to Select Balls from Four Distinct Boxes

Consider 4 boxes, where each box contains 3 red balls and 2 blue balls. Assume that all 20 balls are distinct. In how many different ways can 10 balls be chosen from these 4 boxes so that from each box at least one red ball and one blue ball are chosen ?

Options

A

21816

Correct
B

85536

C

12096

D

156816

Step-by-Step Solution

To find the total number of ways to select 1010 balls from 44 distinct boxes such that at least one red ball and one blue ball are chosen from each box, let us analyze the possible selections from a single box.

Step 1: Ways to choose kk balls from a single box

Each box contains 33 red balls and 22 blue balls (all distinct).

Let rr be the number of red balls and bb be the number of blue balls chosen from a box. We are given 1≤r≤31 \le r \le 3 and 1≤b≤21 \le b \le 2. The total number of balls chosen from one box is k=r+bk = r + b.

Let W(k)W(k) be the number of ways to select kk balls from a single box satisfying the condition:

  1. For k=2k = 2:

    • r=1,b=1r = 1, b = 1: W(2)=(31)×(21)=3×2=6W(2) = \binom{3}{1} \times \binom{2}{1} = 3 \times 2 = 6
  2. For k=3k = 3:

    • r=1,b=2r = 1, b = 2: (31)×(22)=3×1=3\binom{3}{1} \times \binom{2}{2} = 3 \times 1 = 3
    • r=2,b=1r = 2, b = 1: (32)×(21)=3×2=6\binom{3}{2} \times \binom{2}{1} = 3 \times 2 = 6
    • W(3)=3+6=9W(3) = 3 + 6 = 9
  3. For k=4k = 4:

    • r=2,b=2r = 2, b = 2: (32)×(22)=3×1=3\binom{3}{2} \times \binom{2}{2} = 3 \times 1 = 3
    • r=3,b=1r = 3, b = 1: (33)×(21)=1×2=2\binom{3}{3} \times \binom{2}{1} = 1 \times 2 = 2
    • W(4)=3+2=5W(4) = 3 + 2 = 5
  4. For k=5k = 5:

    • r=3,b=2r = 3, b = 2: (33)×(22)=1×1=1\binom{3}{3} \times \binom{2}{2} = 1 \times 1 = 1
    • W(5)=1W(5) = 1

Step 2: Distribution of 10 balls among 4 boxes

Let k1,k2,k3,k4k_1, k_2, k_3, k_4 be the number of balls selected from Box 1, Box 2, Box 3, and Box 4, respectively. We must have: k1+k2+k3+k4=10where 2≤ki≤5 for each i∈{1,2,3,4}k_1 + k_2 + k_3 + k_4 = 10 \quad \text{where } 2 \le k_i \le 5 \text{ for each } i \in \{1, 2, 3, 4\}

Let ki=2+xik_i = 2 + x_i, where xi≥0x_i \ge 0. Substituting this gives: x1+x2+x3+x4=10−8=2x_1 + x_2 + x_3 + x_4 = 10 - 8 = 2

The possible integer distributions of (x1,x2,x3,x4)(x_1, x_2, x_3, x_4) are:

Case 1: One xi=2x_i = 2 and three xi=0x_i = 0

This corresponds to selecting (4,2,2,2)(4, 2, 2, 2) balls from the four boxes in some order.

  • The number of ways to assign these counts to the 4 distinct boxes is: 4!1! 3!=4\frac{4!}{1! \, 3!} = 4
  • For each assignment, the number of ways to choose the balls is: W(4)×W(2)3=5×63=5×216=1080W(4) \times W(2)^3 = 5 \times 6^3 = 5 \times 216 = 1080
  • Total ways for Case 1: 4×1080=43204 \times 1080 = 4320

Case 2: Two xi=1x_i = 1 and two xi=0x_i = 0

This corresponds to selecting (3,3,2,2)(3, 3, 2, 2) balls from the four boxes in some order.

  • The number of ways to assign these counts to the 4 distinct boxes is: 4!2! 2!=6\frac{4!}{2! \, 2!} = 6
  • For each assignment, the number of ways to choose the balls is: W(3)2×W(2)2=92×62=81×36=2916W(3)^2 \times W(2)^2 = 9^2 \times 6^2 = 81 \times 36 = 2916
  • Total ways for Case 2: 6×2916=174966 \times 2916 = 17496

Step 3: Total Number of Ways

Total Ways=4320+17496=21816\text{Total Ways} = 4320 + 17496 = 21816

Thus, the correct option is (A).

Ways to Select Balls from Four Distinct Boxes | Mathematics PYQ Solution - JEE Challenger