A triathlete swims 3 km in 1 hr. Then bikes 50 km in 3 hrs. Finally, the triathlete runs 12 km in 1 hr. What is the triathlete's average speed? Show how you got your answer.

Let $d$ be the length of one segment of the race.

Average speed is total distance divided by total time. The total distance is $3d$, and the total time is $\frac{d}{3}+\frac{d}{20}+\frac{d}{10}=\frac{29d}{60}$.

Thus, the average speed is $3d\div\left(\frac{29d}{60}\right)=\frac{180}{29}$. This is closest to $6$, so the answer is $\mathrm{(D)}$

step-by-step explanation: