The sum of two natural numbers is 11. What is the greatest product that can be obtained with these numbers?
(a) 30
(b) 22
(c) 66
(d) 24
(e) 28
The correct option is (a).

It is enough to examine the products of the natural numbers whose sum is 11.

$$
\begin{array}{llllll}
11=1+10 & \text { and } & 1 \times 10=10 & 11=2+9 & \text { and } & 2 \times 9=18 \\
11=3+8 & \text { and } & 3 \times 8=24 & 11=4+7 & \text { and } & 4 \times 7=28 \\
11=5+6 & \text { and } & 5 \times 6=\mathbf{3 0} & & &
\end{array}
$$