Asked by Anish Panda
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?
Answers
Answered by
Reiny
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
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
Answered by
Anish Panda
I checked that answer, Reiny, and it wasn't right
Answered by
Cheek Slapper
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.
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.
Answered by
Akshath
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.
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