Arithmatical - Time and Distance

DIRECTIONS : Problems based on time and distance.
16. A man in a train notices that he can count 21 telephone posts in one minute. If they are known to be 50 metres apart, then at what speed is the train travelling?
  A.  55 km/hr
  B.  57 km/hr
  C.  60 km/hr
  D.  63 km/hr
Solution
Number of gaps between 21 telephone posts = 20.
Distance travelled in 1 minute= (50 x 20)m
= 1000m
= 1 km.
Speed of the train travelling is = 60 km/hr.
17. A man walking at the rate of 5 km/hr crosses a bridge in 15 minutes. The length of the bridge (in metres) is
  A.  600
  B.  750n
  C.  1000
  D.  1250
Solution
speed= (5x5/18)m/sec
= 25/18 m/sec.
Distance covered in 15 minutes= (25/18 x 15 x 60)m
= 1250 m.
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