Question 922722: Sahara leaves town P and cycles towards town Q, 100 km away, at a speed of 5metres/second. Thirty minutes later, Robert leaves town Q, travelling towards town P at 9metres/second. How long has Robert been travelling when he meets Sandra?
Answer by srinivas.g(540)   (Show Source):
You can put this solution on YOUR website! distance b/w P & Q =100 km
speed of Sahara = 5 meters/second
In 1 second , shara can cover 5 meters
in 1 minute , shara can cover =5*60 =300 meters
in 30 minutes , sahara can cover = 300*30 =9000 meters
=9 KM
By the time Robert leaves Q, sahara has already covered 0.9 km
remaining distance =100 km-9 km =91 KM
speed of Robert = 9 meters/second
Since Robert & Sahara are traveling towards each other , relative speed = 5+9 = 14 meters /second
if they have to meet each other , they together will have to cover 99.1 km with relative speed of 14 meters/second
Time required to cross each other = 
= 
=6500 seconds
So , Robert will have to travel for a duration of 6500 seconds to meet sahara
distance travelled by robert during this time = speed * time
=9*65000
=58500 meters
=58.5 KM
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