Question

A raft was sent away from point A downstream. A patrol-boat left A 5 hour and 20 min later and caught up with the raft 20 km away from point A. What was the speed of the raft if the speed of the patrol-boat was 12 km/hour?

Answer 1

speed of raft ---- x km/h
speed of boat ----12 km/h
when the boat caught up with the raft, they both had gone 20 km
time for raft = 20/x
time for boat = 20/12

20/x - 20/12 = 5 hrs, 20 min = 16/3
times 12x
240 - 20x = 64x

240 = 84x
x = 240/84 km/h = 20/7 km/h

check"
time for raft = 20/(20/7) = 7 hrs
time for boat = 20/12 = 5/3 hrs

difference in time = 7 - 5/3 = 5 1/3 hours
or 5 hours and 20 minutes

Answer 2

I checked that answer, Reiny, and it wasn't right

Answer 3

Hi Anish Panda,

The answer is correct, it's just that you had to round it to 3 km per hour. It would look weird if the answer was 2.86 km.

Answer 4

Reiny, your answer is wrong because in your final answer you have the speed of the raft AND the speed of the current. You forgot to find the current speed.