Answers

2014-03-22T11:52:07+05:30
Let the original speed of car be x km/hr 
now given the distance covered ny car is 840km.
therefore time taken by car = 840/x
now if speed becomes x+10
then time taken will be 8400/x+10
now according to the question 
8400/x-8400/x+10=2
840(1/x - 1/x+10)=2
8400/x^2+10x=2
2x^2+20x-8400=0
x^2+10x-4200=0
solve this equation u will get the original speed
2 5 2
2014-03-22T11:56:38+05:30
The answer is 60km/hr

840/x-840/(x+10)=2
(420x+4200-420x)/x^2+10x=2
x^2+10x-4200=0
x^2+70x-60x-4200=0
(x+70)(x-60)=0
x=60 km/hr
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