A car travels a distance of 840 km at a
uniform speed. If the speed of the car is
10 km/h more, then it takes 2 h less to cover
the same distance. The original speed of the
car was
(a) 45 km/h
(b) 50 km/h
(c) 60 km/h
(d) 75 km/h
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Answer:
Let the original speed of car is x km \hr
Then time taken in moving 840 km=
x
840
hr
if speed is going 10 km \hr more =x+10
Then time taken in moving 840 km=
x+10
840
hr
∴
x
840
−
x+10
840
=2
⇒840(x+10)−840x=2x(x+10)
⇒2x
2
+20x−8400=0
⇒x
2
+70x+−60x−4200=0
⇒(x+70)(x−60)=0
⇒x=60orx=−70
If x=-70 is not true because speed not negetive
So speed is 60 km \ hr
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