Q28 of 46 Page 1

A truck covers a distance of 150 km at a certain average speed and then covers another 200 km at an average speed which is 20 km per hour more than the first speed. If the truck covers the total distance in 5 hours, find the first speed of the truck.

Let the average speed of truck be x km/h


Time taken by truck to complete first 150 KM = t1 (in hours)



Speed after 150 km = (x + 20) km/h


Time taken by truck to next 200 km/h = t2 (in hours)



Given


t1 + t2 = 5 hours




150x + 3000 + 200x = 5x2 + 100x


5x2 - 100x - 3000 = 0


x2 - 20x - 600 = 0


x2 - 60x + 10x - 250 = 0


x(x - 60) + 10(x - 30) = 0


x = 60 or x = - 10 [because in this case time(t1) will be negative, which is not possible]


Average speed of the truck is 60 km/hr.


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