Fill in the blank so that the resulting statement is true.



If you can choose one item from a group of M items and a second item from a group of N items, then the total number of two-item choices is ____.


A$M + N$
B$M \cdot N$
C$N \cdot N$
D$M \cdot M$

Verified Answer :

  • The Fundamental Counting Principle states that the number of ways to perform two independent tasks is the product of the number of ways to perform each task.
  • Choosing one item from a group of \(M\) and one from a group of \(N\) results in \(M \cdot N\) total combinations.
  • The correct choice among the options is \(\boxed{M \cdot N}\).

Explanation

  1. Understand the Fundamental Counting Principle

To determine the total number of ways to choose one item from two different groups, we look at the Fundamental Counting Principle. This principle states that if there are \(M\) ways to perform a first task (choosing an item from the first group) and \(N\) ways to perform a second independent task (choosing an item from the second group), then there are \(M \times N\) ways to perform both tasks together.

  1. Apply the principle to the given groups

In our scenario, we are choosing one item from a group of \(M\) items and one item from a group of \(N\) items. Since each choice is independent, we multiply the number of options for each selection:

  • Number of choices from the first group: \(M\)
  • Number of choices from the second group: \(N\)
  • Total combinations of two-item choices: \(M \times N\).
  1. Identify the correct option

Comparing this result with the given options (\(M+N\), \(M \cdot N\), \(N \cdot N\), and \(M \cdot M\)), we can see that the correct expression is \(M \cdot N\). This confirms that the total number of distinct pairs consisting of one item from the first group and one item from the second group is the product of the sizes of the two groups.

Examples

The counting principle is essential for organizing real-world logistics. For example, if you are designing a lunch menu with \(M=5\) different types of sandwiches and \(N=4\) different types of sides, the total number of unique lunch combinations is \(5 \times 4 = 20\). Understanding this allows you to quickly calculate the variety of combinations in any scenario involving sets of choices.