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Shubham

· started a discussion

· 1 Months ago

Question error. (Question:135063.0)

we can only use the mentioned formula when it is given that the distance traveled by truck and train is equal.

Question:
The ratio between the speeds of a truck, car and train is 3 : 8: 12. The car moved uniformly and covered a distance of 1040 km in 13 hours. What is the average speed of the truck and the train together?
Options:
A) 74 km/h 
B) 60 km/h
C) 48 km/h
D) Cannot be determined
Solution:

Ans (c) 

The ratio between the speeds of the truck, car and train is 3: 8: 12.

Given that the car covers 1040 km in 13 hours, the speed of the car 80 km/h

Also, if we assume that the speeds of the truck, car and train are 3x, 8x and 12x 

respectively, then

Speed of car = \(\cfrac{1040}{13}\) = 80 kmph

Ratio of speed of truck, car and train = 3 : 8 : 12

Now, 8x = 80 => x = 10 

Hence, truck = 30 kmph 

Train = 120 kmph

Therefore, Average speed of truck and train together = \(=\cfrac{2\times x\times y}{x+y}\)

=\(=\cfrac{2\times 30\times 120}{30+120}=48km/h\)

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