Answer
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 $M\cdot N$.
Work Step by Step
We have two groups having M and N items.
Now, if we want to choose one item from the first group then we will have M number of choices and if we want to choose one from the second group then we will have N number of choices. Thus, the total number of choices would be the multiplication of M and N, that is $M\times N$.
