Question

If the speed of a car is decreased by 8km/h, it takes 1 hour more to cover a distance of 240km. find the original speed of the car​

Answer 1

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If the speed of the car is decreased by 8 km per hour, it takes 1 hour more to cover a distance of 240 km. What is the original speed of the car?

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4 Answers



C. S. Sharma, Most Viewed Writer, Quora, Mathematics Word Problems

Answered January 16, 2020

Friends….!

Let the speed of the car be x km per hour

Distance = 240 km

Speed of car = x km per hour

Time = Distance/speed

Time = 240/x

If the speed of the car is decreased by 8 km per hour, it takes 1 hour more to cover a distance of 240 km

Time during changed speed

= 240 km /x - 8 km per hour

240/(x - 8) - 240/x = 1 hour

240x —240 (x - 8)/ x (x - 8) = 1 hour

240x — 240x + 1920/ x^2 - 8x = 1 hour

1920/x^2 - 8x = 1 hour

Cross multiplication

x^2 - 8x = 1920

x^2 - 8x -1920 = 0

x^2 - 48x + 40 x - 1920

x (x - 48) + 40 (x - 48)

(x + 40) (x - 48)

x = —40 is not possible being negative hence discarded

x = 48 km per hour

The original speed of the car was 48 km per hour

Answer : the original speed of the car was 48 km per hour

773 views · Answer requested by Prakash Kumar



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Biju P.S, former 15 Years Experience in Sales in FMCG Companies

Answered January 16, 2020

Let s & t be the original speed & time taken.

So s×t = 240

t = 240/s

Also (s - 8)(t+1) = 240

st+s-8t-8 = 240

Applying the value of st & t in above equation

240+s-8×240/s-8 = 240

s -1920/s = 8

s²-1920 = 8s

s²-8s-1920 = 0

(s-48)(s+40) = 0

So s = 48 or -40

Since s can not be negative, s = 48

So original speed of the car is 48 km/hr

108 views

Answer 2

Answer:

Let the speed of car be xkmph

Let it takes Time t hrs to cover the

distance of 240km

⟹xt=240⋯(1)

speed is decreased by 8⟹x−8

Time is increased by 1⟹t+1

it covers the same distance so (x−8)(t+1)=240

xt+x−8t−8=240

From (1)⟹x−8t−8=0

x=8t+8

Put it in (1)⟹(8t+8)(t)=240

t ² +t−30=0

t ²+6t−5t−30=0

t(t+6)−5(t+6)=0

(t−5)(t+6)=0

t=5,−6

Time cannot be negative so t=5

Put it in (1)

⟹x(5)=240⟹x=12kmph

I hope it help you..