Trains Boats and Streams Practice Test 4 with solutions

Question : 11 of 40

Marks: +1, -0

A train travelled the first 150 km at 10 km/hour faster than the usual speed, but it returned the same distance at 10 km/hr slower than the usual speed. If the total time taken by the train is 8 hours, for how many hour and it travels at the faster speed?

Validate

Solution:

Let the usual speed = x km/hour
Faster speed = (x + 10) km/hour
Slower speed = (x - 10) km/hour

{150}/{x+10}+{150}/{x-10}

= 8

{x-10+x-10}/{x^2-100}

8/{150}

150x =

4x^2 - 400

2x^2

- 75x - 200 = 0

2x^2

- 80x + 5x - 200 = 0
(2x + 5) (x - 80) = 0
⇒ x = 80

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