Keegan paddled the first $12 \mathrm{~km}$ of his $36 \mathrm{~km}$ kayak trip before lunch. What fraction of his overall trip remains to be completed after lunch?
(A) $\frac{1}{2}$
(B) $\frac{5}{6}$
(C) $\frac{3}{4}$
(D) $\frac{2}{3}$
(E) $\frac{3}{5}$
Keegan paddled $12 \mathrm{~km}$ of his $36 \mathrm{~km}$ trip before lunch.

Therefore, Keegan has $36-12=24 \mathrm{~km}$ left to be completed after lunch.

The fraction of his trip remaining to be completed is $\frac{24}{36}=\frac{2}{3}$.

ANSWER: (D)