1)Speed of boat in still water is 20 km/hr. If the speed of the stream is 8 km/hr, find its downstream and upstream speeds ?

A)20,5

B)20,12

C)28,12

D)18,10

Answer:C)28,12

Explanation:
Here
u=20
v=8
Downstream Speed = u + v = 20 + 8 = 28 km/hr
Upstream Speed = u - v = 20 -8 = 12 km/hr

2) A man can row downstream at 24 km/hr and upstream at 16 km/hr. Find his speed in still water and the rate of the current.

A)20,4

B)20,2

C)15,3

D)16,4

Answer:A)20,4

Explanation:
Speed of the boat or swimmer in still water
= 1/2 * (Downstream Speed + Upstream Speed)
= 1/2 * (24+16)
= 20 km/hr
Speed of the current
= 1/2 * (Downstream Speed - Upstream Speed)
= 1/2 * (24-16)
= 4 km/hr

3) The speed of the boat in still water is 18 km/hr. It takes twice as long as to go upstream to a point as to return downstream to the starting point. What is the speed of the current?

A)4 km/hr

B)3 km/hr

C)6 km/hr

D)4 km/hr

Answer:C)6 km/hr

Explanation:
Let speed of the current = x km/hr.
As per question,
Downstream Speed = 2*Upstream speed
18 + S = 2(18 - S)
S = 6 km/hr

4) A boat can travel with a speed of 15 km/hr in still water. If the speed of the stream is 9 km/hr, find the time taken by the boat to go 72 km downstream.

A)2 hours

B)3 hours

C)4 hours

D)5 hours

Answer:B)3 hours

Explanation:
Speed downstream
= (15 + 9) km/hr
= 24 km/hr.
Time taken to travel 68 km downstream
= 72/24 hrs
= 3 hrs.

5)In one hour, a boat goes 16 km/hr along the stream and 10 km/hr against the stream. The speed of the boat in still water (in km/hr) is:

Answer:13 kmph.

Explanation:
Speed in still water = 1/2(16+10) kmph
= 13 kmph.