a boat travels with a speed of 15 km per hour in still water if a river flowing at 5 km per hour the boat travel some distance downstream and then returns. the ratio of average speed to the speed in still water is:
a) 8:3
b) 3:8
c) 8:9
d) 9:8
Answers
Answered by
36
Let the distance travelled be x km
speed downstream = 15+ 5 = 20km/h
speed upstream = 15-5 = 10 km/h
Total distance = 2x
Total time = x/20 + x/10 = 3x/20
Average speed = Total distance/Total time
= 2x / (3x/20)
= 40/3
The ratio of average speed to the speed in still water = 40/3 : 15
= 40 : 45
= 8 : 9
Choice C
speed downstream = 15+ 5 = 20km/h
speed upstream = 15-5 = 10 km/h
Total distance = 2x
Total time = x/20 + x/10 = 3x/20
Average speed = Total distance/Total time
= 2x / (3x/20)
= 40/3
The ratio of average speed to the speed in still water = 40/3 : 15
= 40 : 45
= 8 : 9
Choice C
Answered by
10
Answer:
Step-by-step explanation:
Let the distance travelled be x km
speed downstream = 15+ 5 = 20km/h
speed upstream = 15-5 = 10 km/h
Total distance = 2x
Total time = x/20 + x/10 = 3x/20
Average speed = Total distance/Total time
= 2x / (3x/20)
= 40/3
The ratio of average speed to the speed in still water = 40/3 : 15
= 40 : 45
= 8 : 9
Choice C
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