Euclid 2020/Problem 2

2. (a) The three-digit positive integer $m$ is odd and has three distinct digits. If the hundreds digit of m equals the product of the tens digit and ones (units) digit of $m$, what is $m$?

(b) Eleanor has 100 marbles, each of which is black or gold. The ratio of the number of black marbles to the number of gold marbles is $1 : 4$. How many gold marbles should she add to change this ratio to $1 : 6$?

(c) Suppose that n is a positive integer and that the value of $\frac{n^2 + n + 15}{n}$ is an integer. Determine all possible values of $n$.