SOLUTION: A ship travel from port A to port B with distance 20 knots in 30 minutes.the ship travel back from port B to port A in 20 minutes. What is the average speed of the round trip in km

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Question 859490: A ship travel from port A to port B with distance 20 knots in 30 minutes.the ship travel back from port B to port A in 20 minutes. What is the average speed of the round trip in km/hr.
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
A ship travel from port A to port B with distance 20 km in 30 minutes.
the ship travel back from port B to port A in 20 minutes.
What is the average speed of the round trip in km/hr.
:
Let a = average speed for the trip in km/h
:
Assuming the one-way distance is 20 km
Change 30 min to 1/2 hr, and 20 min to 1/3 hr
:
Find the speed A-B and B-A
20%2F%281%2F2%29 = 40 km/hr
:
20%2F%281%2F3%29 = 60 km/hr
:
Write a time equation; time = dist/speed
20%2F40 + 20%2F60 = 40%2Fa
Multiply by 120a to clear the denominator, results
3a(20) + 2a(20) = 120(40)
60a + 40a = 4800
100a = 4800
a = 4800/100
a = 48 km/hr av speed for the round trip