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Q.

On a roadway, points C and D are 90 km away from one another. At the same time, one car begins from C and another from D. They will meet in 9 hours if they travel in the same direction, and in 1 2 7   hours if they travel in the opposite direction. What is the speed of both the cars?


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a

40 km/h and 30km/h

b

40 km/h and 50km/h

c

30 km/h and 30km/h

d

20 km/h and 40km/h 

answer is A.

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Detailed Solution

It is given that two points C and D are 90 km away from one another on a roadway. At the same time, one car begins from C and another from D. They will meet in 9 hours if they travel in the same direction, and in 1 2 7   hours if they travel in the opposite direction.
Let’s assume that the speed of the cars starting from C and D be x   km/h and y   km/h. According to the question,
9x90=9y xy=10               (1) and  
9 7 x+ 9 7 y=90 1 7 x+ 1 7 y=10          (2)  
Divide equation (1) by 7 and then add with equation (2), we get,
  1 7 x+ 1 7 x= 10 7 +10 2 7 x= 80 7 x=40   Therefore from equation (1), we have,
xy=10 40y=30 y=30  
Therefore the speed of the car starting from point C = 40 km/h and the speed of the car starting from point D = 30 km/h.
Hence option (1) is correct.
 
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