A.50%

B.40%

C.30%

D.20%

E.None of these

2) A boat rows 46km at a certain speed in the downstream and while returning, the boatman doubles his boat speed. The speed of the boat in still water is 15kmph and the current speed is 5kmph. What is the total time taken by him to cover the total distance?

A.4 hours

B.4.14 hours

C.5 hours

D.5.5 hours

E.None of these

3) Difference between the speed of stream and boat in still water is 14 kmph. If the boat covers 330 km along with stream in 11 hours, then what is the ratio of the speed of boat in still water to stream?

A.8:3

B.10:7

C.11:4

D.12:7

E.None of these

4) 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

5) 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.30.25 kmph

B.35 kmph

C.20.15 kmph

D.15 kmph

E.None of these

Answers :

1) Answer: A

US = x kmph and DS = 3x kmph

24/x + 48/3x = 2

=> x = 20

US = 20 kmph and DS = 60kmph

Speed of boat in still water = (20 + 60)/2 = 40kmph

Speed of stream = (60 – 20)/2 = 20kmph

Required % = 20/40 * 100 = 50%

2) Answer: B

Required time = 46/(15 + 5) + 46/(2 * 15 – 5)

= 46/20 + 46/25 = 4.14 hours

3) Answer: C

Upstream speed = 14 kmph

Downstream speed = 330/11 = 30 kmph

Required ratio = (30 + 14)/2:(30 – 14)/2

= 22:8

= 11:4

4) 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

5) 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