A car travels a distance of 840 km at uniform speed. If

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A car travels a distance of 840 km at uniform speed. If the speed of the car is 10 km/hr more. It takes two hours less to cover the same distance. The original speed of the car was ?

1. 45 km/hr.
2. 50 km/hr.
3. 60 km/hr .
4. 75 km/hr.

Correct Option: C

Let the original speed be x km/hr.
Then, [ 840/x - 840/( x + 10) ] = 2
⇒ 840 (x + 10) - 840x = 2x (x+10)
⇒ x² + 10x - 4200 = 0
⇒ (x + 70) (x - 60 ) = 0
∴ x = 60 km/hr.