Math Problem Statement

There are 5 men and 9 women auditioning to be in the school play. If the cast consists of 2 women and 2 men, how many different casts can be selected? If the cast consists of 2 women or 2 men, how many different casts can be selected?

Solution

Let's go step by step and solve both questions based on the given information.

1. If the cast consists of 2 women and 2 men, how many different casts can be selected?

To solve this, we need to select 2 women from a group of 9 women and 2 men from a group of 5 men. The number of ways to select 2 people from a group is given by combinations, denoted as (nr)\binom{n}{r}, where nn is the total number of people and rr is the number of people to select.

  • For women: (92)=9×82×1=36\binom{9}{2} = \frac{9 \times 8}{2 \times 1} = 36
  • For men: (52)=5×42×1=10\binom{5}{2} = \frac{5 \times 4}{2 \times 1} = 10

Now, multiply the two results to find the total number of different casts:

Total casts=(92)×(52)=36×10=360\text{Total casts} = \binom{9}{2} \times \binom{5}{2} = 36 \times 10 = 360

Answer for Question 1: 360 casts


2. If the cast consists of 2 women or 2 men, how many different casts can be selected?

In this case, we have two separate cases: selecting only 2 women or selecting only 2 men. We need to calculate both cases and then add them, since "or" in probability means addition.

  • For 2 women: (92)=36\binom{9}{2} = 36
  • For 2 men: (52)=10\binom{5}{2} = 10

Adding the two results:

Total casts=(92)+(52)=36+10=46\text{Total casts} = \binom{9}{2} + \binom{5}{2} = 36 + 10 = 46

Answer for Question 2: 46 casts


Would you like further clarification on any step? Here are 5 related questions you might be interested in:

  1. How are combinations different from permutations?
  2. How do you calculate combinations for larger groups?
  3. What if the cast required 3 women and 2 men? How would you approach that?
  4. How do combinations change when there's no gender restriction?
  5. What if the requirement was 2 women and/or 2 men, including mixed genders?

Tip: When using combinations, remember that order does not matter in the selection.

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Math Problem Analysis

Mathematical Concepts

Combinations
Counting Principles

Formulas

Combination formula: C(n, r) = n! / (r!(n - r)!)

Theorems

Basic Counting Principle
Combination Theorem

Suitable Grade Level

Grades 9-11