By increasing the speed of a car by 100 km/h ,the time of journey of 72 km is reduced
by 36 minutes .Find the original speed of car.
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Answer:
orignal speed 30km /hr
Step-by-step explanation:
Let original speed be x km/hr.
∴ Time = 72/x hr
New speed = x + 10 km/hr.
∴ New time = 72/x + 10 hr
Difference in time = 36 mins
∴ 72/x - 72/x + 10 = 36/60
72x + 720 – 72x/x(x + 10) = 3/5
5 × 720 = 3(x2 + 10x)
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
as x = - 40 is not acceptable
∴ Original speed = 30 km/hr.
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