John covers a part of the journey at 20 km/hr and the remaining at 70 km/hr, taking total of 8 hours to cover the distance of 400 km, How many hours he has been driving at 20 km/hr?

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Solution

Let the total time he travelled with a speed of $20 k m h^{- 1}$ is $x hr.$

So time taken to cover a distance with $70 k m h^{- 1}$ $= 8-x$
Total distance covered, $= 400 k m$

So, from, $d i s t a n c e = s p e e d \times t i m e$
The total distance traveled, $20x + 70(8-x) =400$
$20 x + 560 - 70 x = 400 ⟹ 50 x = 160$
$x = \frac{160}{50} = 3.2 h r$

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Q. John covered a part of his journey at

20 kmph

, and the remaining part at

70 kmph

. He took a total of

8 hr

to cover a distance of

400 km

. For how much time did he travel at

20 kmph

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John covers a part of the journey at 20 km/hr and the remaining at 70 km/hr, taking total of 8 hours to cover the distance of 400 km, How many hours he has been driving at 20 km/hr?

Let the total time he travelled with a speed of 20kmh−1 is x hr. So time taken to cover a distance with 70kmh−1 = 8-x Total distance covered, =400km So, from, distance=speed×time The total distance traveled, 20x + 70(8-x) =400 20x+560−70x=400⟹50x=160x=16050=3.2hr