A.11 hours

B.13 hours

C.15 hours

D.17 hours

E.None of these

2) The speed of upstream is 12 kmph. If the speed of boat is decreased by 40% and the speed of stream is increased by 50%, then the boat covers 78 km downstream in 5 hours. Find the original speed of stream?

A.5 kmph

B.6 kmph

C.3 kmph

D.4 kmph

E.8 kmph

3) The ratio of the speed of the boat in downstream to upstream is 7: 4. A boy takes 4 hours to cover the total distance of 88km upstream. What is the speed of the boat in still water?

A.30.25kmph

B.35kmph

C.20.15kmph

D.15kmph

E.None of these

4) Nirmal can row downstream 45 km in 5 hours and upstream 15 km in 3.75 hours, then what is the ratio of speed of current to speed of boat?

A.2:3

B.3:5

C.4:7

D.7:11

E.None of these

5) The boat will take 2 hours to cover the distance of 20km in downstream and while covering the same distance in upstream it will take 5 hours. Find the speed of the stream.

A.2kmph

B.3kmph

C.4kmph

D.5kmph

E.None of these

Answers :

1) Answer: D

Speed of upstream = 128/16 = 8 kmph

Speed of boat = 3x

Speed of stream = 3x * 100/300 = x

3x – x = 8

x = 4

Downstream speed = 3x + x = 4 * 4 = 16 kmph

Required time = 272/16

= 17 hours

2) Answer: D

Speed of boat = x

Speed of stream = y

x – y = 12 ----(1)

78/(x * 60/100 + y * 150/100) = 5

3x + 7.5y = 78 ----(2)

From (1) and (2)

10.5y = 42

y = 4

3) Answer: A

Speed in upstream = 88/4 = 22kmph

Speed in downstream = 7/4 * 22 = 38.5kmph

Speed of the boat in still water = (22 + 38.5)/2 = 30.25kmph

4) Answer: E

Downstream speed = 45/5 = 9 kmph

Upstream speed = 15/3.75 = 4 kmph

Required ratio = (9 – 4)/2:(9 + 4)/2

= 5:13

5) Answer: B

Downstream speed=20/2=10kmph

Upstream speed=20/5=4kmph

Speed of the stream =1/2*(10-4)=3kmph