# boats and streams aptitude questions

1.

A boat can travel with a speed of 13 km/hr in still water. If the speed of the stream is 4 km/hr, find the time taken by the boat to go 68 km downstream.
A.     2 hours    B.     3 hours
C.     4 hours    D.     5 hours

Explanation:

Speed downstream = (13 + 4) km/hr = 17 km/hr.

Time taken to travel 68 km downstream =         68     hrs = 4 hrs.
17

2.

A man’s speed with the current is 15 km/hr and the speed of the current is 2.5 km/hr. The man’s speed against the current is:
A.     8.5 km/hr    B.     9 km/hr
C.     10 km/hr    D.     12.5 km/hr

Explanation:

Man’s rate in still water = (15 – 2.5) km/hr = 12.5 km/hr.

Man’s rate against the current = (12.5 – 2.5) km/hr = 10 km/hr.

3.

A boat running upstream takes 8 hours 48 minutes to cover a certain distance, while it takes 4 hours to cover the same distance running downstream. What is the ratio between the speed of the boat and speed of the water current respectively?
A.     2 : 1    B.     3 : 2
C.     8 : 3    D.     Cannot be determined
E.     None of these

Explanation:

Let the man’s rate upstream be x kmph and that downstream be y kmph.

Then, distance covered upstream in 8 hrs 48 min = Distance covered downstream in 4 hrs.

x x 8     4         = (y x 4)
5

44     x =4y
5

y =     11     x.
5

Required ratio =         y + x         :         y – x
2     2

=         16x     x     1         :         6x     x     1
5     2     5     2

=     8     :     3
5     5

= 8 : 3.

4.

A motorboat, whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is:
A.     4    B.     5
C.     6    D.     10

Explanation:

Let the speed of the stream be x km/hr. Then,

Speed downstream = (15 + x) km/hr,

Speed upstream = (15 – x) km/hr.

30     +     30     = 4     1
(15 + x)     (15 – x)     2

900     =     9
225 – x2     2

9×2 = 225

x2 = 25

x = 5 km/hr.

5.

In one hour, a boat goes 11 km/hr along the stream and 5 km/hr against the stream. The speed of the boat in still water (in km/hr) is:
A.     3 km/hr    B.     5 km/hr
C.     8 km/hr    D.     9 km/hr