Question:medium

In how many ways can 8 identical pens be distributed among Aal, Bal, and Cal so that Aal gets at least 1 pen, Bal gets at least 2 pens, and Cal gets at least 3 pens?

Show Hint

For distribution of identical items with minimum constraints, reduce the variables to non-negative and use stars and bars.
Updated On: Jun 15, 2026
  • 4
  • 2
  • 3
  • 6
  • 5
Show Solution

The Correct Option is D

Solution and Explanation

Step 1: Understanding the Concept:
This is a distribution problem of identical items into distinct groups with lower bounds. We use the "Stars and Bars" method.
Step 2: Key Formula or Approach:
Formula: \( \binom{n + r - 1}{r - 1} \) where \(n\) is the number of remaining items after satisfying the minimum requirements and \(r\) is the number of groups.
Step 3: Detailed Explanation:
1. Total pens = 8. 2. Minimum requirements: Aal \(\ge 1\), Bal \(\ge 2\), Cal \(\ge 3\). 3. First, give the minimum number of pens to each: Pens given = \(1 + 2 + 3 = 6\) pens. 4. Remaining pens to distribute freely = \(8 - 6 = 2\) pens. 5. Distribute \(n=2\) identical pens among \(r=3\) people: Ways = \( \binom{2 + 3 - 1}{3 - 1} = \binom{4}{2} \). 6. Calculation: \( \binom{4}{2} = \frac{4 \times 3}{2 \times 1} = 6 \).
Step 4: Final Answer:
There are 6 ways to distribute the pens.
Was this answer helpful?
0