Answer :
The speed of the raft if the speed of the patrol-boat was 12 km/hour, and it caught the raft in 5 hours 20 min later is 2.857 km/hours.
What is the speed of a body?
The speed of a body is the rate at which it covers the total distance is in the time taken. The speed of the body is given as,
[tex]S=\frac{D}{T}[/tex]
Here, (d) is the distance travelled by the body, and (t) is time taken by the body to cover that distance.
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.
Total time the patrol boat took in hours is,
[tex]T = 5 + \frac{20}{60}[/tex]
T=5+0.3333
T=5.3333 hours
The speed of the patrol boat is 12 km/hour, and it caught up with the raft 20 km away from point A. Thus, the time taken with this speed to cover 20 km distance is,
[tex]T=\frac{20}{12}[/tex]
T=1.6667 Hours
Thus, the total time is,
T=5.3333+1.6667
T=7 Hours
Now as the raft travel 20 km in 7 hours. Therefore, find the speed of raft by putting the values in above formula as,
[tex]S=\frac{20}{7}[/tex]
S=2.857 kmph