Question

A man travels 370 km partly by train and partly by car. If he covers 250 km by train and the rest by car, it takes him 4 hours. But, if he travels 130 km by train and the rest by car, he takes 18 minutes longer. Find the speed of the train and that of the car.

Solution

Let the speed of the train be x km/hr and that of the car be y km/hr.
We have following cases :
Case I. When he travels 250 km by train and the rest by car:
In this case, we have
Time taken by the man to travel 250 km by train
$equals 250 over straight x hrs$
Time taken by the man to travel (370 - 250)
$space space space space space space space space space equals 120 space km space by space car space equals space 120 over straight y hrs$
According to the given condition
$250 over straight x plus 120 over straight y equals 4 rightwards double arrow space space 125 over straight x plus 60 over straight y equals 2$

Case II. When he travels 130 km by train and the rest by car:
Time taken by the man to travel 130 km by train
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Time taken by the man to travel (370 - 130)
$equals space 240 space km space by space car space equals space 240 over straight y hrs$

According to the given condition

$130 over straight x plus 240 over straight y equals 4 space space hrs space 18 space minutes rightwards double arrow space 130 over straight x plus 240 over straight y equals 4 18 over 60 rightwards double arrow space space 130 over straight x plus 240 over straight y equals 43 over 10$

Thus, we have following system of equations :
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$Putting space 1 over straight x equals straight u space and space 1 over straight y equals straight v comma space t h e space a b o v e space s y s t e m space r e d u c e s space t o$
125u + 60 v = 2 ....(i)
130u + 240v = $43 over 10 space space space space space space space space space space space space space space space space space.... left parenthesis ii right parenthesis$
Multiplying equation (iii) by 4 the above system of equations becomes
500u + 240v = 8 ...(iii)
130u + 240v = $space space space 43 over 10 space space space space space space space space space space space space... left parenthesis iv right parenthesis$
Subtracting equation (vi) from equation (iv), we get
$370 straight u space equals space 8 space minus 43 over 10 rightwards double arrow space space 370 straight u space equals space 37 over 10 rightwards double arrow space straight u equals 1 over 100 Putting space straight u space equals space 1 over 100 space in space equatiion space left parenthesis iii right parenthesis comma space we space get$
5 + 240v = 8
$space space space space space space rightwards double arrow space 240 straight v space equals space 3 space rightwards double arrow space straight v space equals space 1 over 80 space space space space Now comma space space space space straight u space equals space 1 over 100 space and space straight v space 1 over 80 space space space space rightwards double arrow space space space space space space space 1 over straight x equals 1 over 100 space and space 1 over straight y equals space 1 over 80 space space space space rightwards double arrow space space space space space space space straight x space equals space 100 space space and space straight y space equals space 80$

Hence, Speed of the train = 100 km/hr
Speed of the car = 80 km/hr.

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Pair Of Linear Equations In Two Variables

A man travels 370 km partly by train and partly by car. If he covers 250 km by train and the rest by car, it takes him 4 hours. But, if he travels 130 km by train and the rest by car, he takes 18 minutes longer. Find the speed of the train and that of the car.

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