Arithmatical - Boat’s and Streams

DIRECTIONS : Problems based on Boats and Streams.
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
Solution
Speed Downstream= (13 + 4) km/hr
= 17 km/hr.
Time taken to travel 68 km downstream=(68 / 17)hrs
= 4 hrs.
2. The speed of a boat in still water is 15 km/hr and the rate of current is 3 km/hr. The distance travelled downstream in 12 minutes is
  A.  1.2 km
  B.  1.8 km
  C.  2.4 km
  D.  3.6 km
Solution
Speed Downstream= (15 + 3) km/hr
= 18 km/hr.
Distance travelled=(18 x 12/60)hrs
= 3.6km.

3. A boat takes 19 hours for travelling downstream from point A to point B and coming back to a point C midway between A and B. If the velocity of the stream is 4 kmph and the speed of the boat in still water is 14 kmph, what is the distance between A and B ?
  A.  160 km
  B.  180 km
  C.  200 km
  D.  220 km
Solution
Speed Downstream= (14 + 4) km/hr
= 18 km/hr.
Speed upstream=(14 - 4) km/hr
= 10 km/hr..
Let the distance b/w A and B
be xkm.Then
=(x/18+ x/2 / 10)
= 19
= 19x / 180 = 19
x= 180.
4. A boat running downstream covers a distance of 16 km in 2 hours while for covering the same distance upstream, it takes 4 hours. What is the speed of the boat in still water?
  A.  4 km/hr
  B.  6 km/hr
  C.  8 km/hr
  D.  Data inadequate
Solution
Rate Downstream= (16 / 2) kmph
= 8 kmph
Rate upstream=(16 / 4) kmph
= 4 kmph.
Speed in still water= 1 / 2 (8 + 4)kmph
= 1/2 x 12
= 6 kmph.
5. A man can row upstream at 8 kmph and downstream at 13 kmph. The speed of the stream is
  A.  2.5 km/hr
  B.  4.2 km/hr
  C.  5 km/hr
  D.  10.5 km/hr
Solution
Speed of stream= 1 / 2 (13 - 8 )kmph
= 1/2 x 5
=5 /2
= 2.5
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