Math Problem Statement

A group of 2 students is to be chosen from a 30-member class to represent the class on the student council. How many ways can this be done? (NOTE: Order of the selection is not important.)

Answer: ways

Solution

Since the order of selection is not important, we are dealing with a combination problem. The formula for combinations is:

C(n,r)=n!r!(nr)!C(n, r) = \frac{n!}{r!(n - r)!}

In this case:

  • n=30n = 30 (the total number of students),
  • r=2r = 2 (the number of students to be chosen).

Substitute these values into the formula:

C(30,2)=30!2!(302)!=30!2!28!C(30, 2) = \frac{30!}{2!(30 - 2)!} = \frac{30!}{2! \cdot 28!}

Simplify this expression by canceling 28!28! from the numerator and denominator:

C(30,2)=30×292×1=8702=435C(30, 2) = \frac{30 \times 29}{2 \times 1} = \frac{870}{2} = 435

So, there are 435 ways to choose 2 students from a class of 30.

Answer: 435 ways

Would you like a further breakdown or explanation?


  1. How would the calculation change if we had to select 3 students instead of 2?
  2. How many ways can we select a group of 5 students from the same class?
  3. What if the order of selection mattered? How many ways could 2 students be chosen then?
  4. Can you calculate the number of ways to choose 2 students from a class of 50?
  5. How would the approach differ if we had 10 students and needed to form a team of 4?

Tip: When the order of selection doesn't matter, always use combinations, not permutations.

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Math Problem Analysis

Mathematical Concepts

Combinations
Counting Principles

Formulas

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

Theorems

Combination theorem for selection without regard to order

Suitable Grade Level

Grades 10-12