Sam bicycles at $16 \mathrm{~km} / \mathrm{h}$ and Chris bicycles at $24 \mathrm{~km} / \mathrm{h}$. At noon, Sam is $1 \mathrm{~km}$ north of Chris, and each begins to ride north. How many minutes will it take for Chris to catch Sam?
(A) $1 \frac{1}{2}$
(B) $2 \frac{1}{2}$
(C) $3 \frac{3}{4}$
(D) $7 \frac{1}{2}$
(E) 8
Since Chris bicycles at $24 \mathrm{~km} / \mathrm{h}$ and Sam bicycles at $16 \mathrm{~km} / \mathrm{h}$, then Chris gains $8 \mathrm{~km} / \mathrm{h}$ on Sam.

Since Sam starts $1 \mathrm{~km}$ north of Chris, then it takes Chris $\frac{1}{8}$ of an hour, or $\frac{1}{8} \times 60=\frac{60}{8}=\frac{15}{2}$ or $7 \frac{1}{2}$ minutes to catch Sam.