A jet ski can go 12 mph in still water. If a rider goes upstream for 5 hours against a current of 5 mph, how long will it take the rider to return? ( Hint: Upstream speed is (12 - 5) mph; how far can the rider go in 5 hours?
)
A) $1 \frac { 1 } { 17 } \mathrm { hr }$
B) $3 \frac { 1 } { 17 } \mathrm { hr }$
C) $2 \mathrm { hr }$
D) $5 \mathrm { hr }$
E) $2 \frac { 1 } { 17 } h$

Question

Quizplus · Accepted Answer

Upstream speed = jet ski speed - current speed = 12 mph - 5 mph = 7 mph

In 5 hours, the rider can travel 7 mph x 5 hrs = 35 miles upstream.

To return, the rider will have the current with them, so their speed will be:

Downstream speed = jet ski speed + current speed = 12 mph + 5 mph = 17 mph

To travel 35 miles at 17 mph, the rider will need:

time = distance / speed = 35 miles / 17 mph = 2 1/17 hours

Therefore, the answer is E.

A Jet Ski Can Go 12 Mph in Still Water 1117hr1 \frac { 1 } { 17 } \mathrm { hr }1171​hr

A Jet Ski Can Go 12 Mph in Still Water $1 \frac { 1 } { 17 } \mathrm { hr }$