Question

7 By increasing the speed of a car by 10 km/hr, the time of journey for a
distance of 72 km is reduced by 36 minutes. Find the original speed of
car​

Answer 1

Answer:

30 km/hr

Step-by-step explanation:

By increasing the speed of car by 10km/hr, the time of journey for a distance of 72 km is reduced by 36 min.

Let original speed of the car =  x km/hr

distance = 72 km

time taken = distance / speed =  72/x hr

increased speed = x + 10 km/hr

Time taken with increased speed = 72/(x + 10) hr

72/x  - 72/(x + 10)  = 36/60

=> 1/x  - 1/(x + 10)  =  1/120

=> (x + 10) - x = x(x+10)/120

=> 1200 = x² + 10x

=> x² + 10x - 1200 = 0

=> x² + 40x - 30x -1200 = 0

=> x(x + 40) - 30(x + 40) = 0

=> (x-30)(x+40) = 0

=> x = 30   x = -40 is neglected as speed can not be negative

∴ original speed of the car = 30 km/hr//

Please mark as brainliest