Question 130928
Solution - 
  Let the speed of the car be x miles/hour
  and the speed of train be y miles/hour
  According to first condition
  that is speed of the car is twice the speed of the train
   x = 2y       ..... (i)
  According to the second condition 
  time taken by car to cover 300 miles = distance/speed
                                       = 300/x
  time taken by train to cover 300 miles = 300/y
  now car arrives 7.5 hours before train
  therefore
         300/x + 7.5 = 300/y  (since train takes 7.5 hours more than car therefore we will add 7.5 hours with the time of the car to equate the value)
    now substituting the value of x from equation (i) we have
        300/2y +7.5 = 300/y
 now transfering the like terms on one side we have
 7.5 = 300/y - 300/2y
  75/10 = (600 - 300)/2y
   75/10 = 300/2y
   15/2 = 150/y
 now by cross multiplicationb we have
  15y = 300
    y = 300/15
    y = 20
 now substituting the value of y in equation (i) we have
    x = 2y
    x = 2*20
    x = 40
 therefore the speed of the train is y miles/hour = 20 miles/hour
  and speed of car is x miles/hour = 40 miles/hour
 
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