Yvon has 4 different notebooks and 5 different pens. He must bring exactly one notebook and exactly one pen to his class. How many different possible combinations of notebooks and pens could he bring?
(A) 9
(B) 16
(C) 20
(D) 10
(E) 5
Solution 1

For each of the 4 different notebooks that Yvonn may choose, there are 5 different pens that may be chosen. Thus, there are $4 \times 5=20$ possible combinations of notebooks and pens that he could bring to class.

## Solution 2

We begin by naming the 4 notebooks $A, B, C, D$, and numbering the 5 pens $1,2,3,4,5$. If Yvonn chooses notebook $A$ and pen number 1, then we may call this combination $A 1$. If Yvonn chooses notebook $A$, he may instead choose one of the pens numbered 2, 3, 4, or 5 . If Yvonn chooses notebook $A$, he has a total of 5 possible combinations: $A 1, A 2, A 3, A 4, A 5$. Similarly, Yvonn has 5 pen choices for each choice of notebook.

These remaining possible combinations are: $B 1, B 2, B 3, B 4, B 5, C 1, C 2, C 3, C 4, C 5, D 1, D 2$, $D 3, D 4, D 5$.

Thus, there are 20 possible combinations of notebooks and pens that Yvonn could bring to class.

ANswer: (C)