$28 \cdot 16$ A person has pennies, nickels, dimes, quarters, and half-dollars totaling $2.73. If he has an equal number of each type of coin, then the total number of coins he has is
(A) 3 .
(B) 5 .
(C) 9 .
(D) 10 .
(E) 15 .
(28th American High School Mathematics Examination, 1977)
［Solution］If $n$ is the number of each type of coin this person has, then
$$
(1+5+10+25+50) n=273,
$$

solving for $n$ gives $n=3$.
There are 3 of each of the five types of coins, making a total of 15 coins.
Therefore, the answer is $(E)$.