Question

A car covers 1/5 of the distance from a to b at the speed of 8 km/hour, 1/10 of the distance at 25 km per hour and the remaining at the speed of 20 km per hour. Find the average speed of the whole journey

Answer 1

Answer:

speed= distance ÷ time.Calcute according to the formula

Answer 2

The average speed of the whole journey is 15.625 km/h.

Explanation:

Let the total distance to be covered is 1 km. Total time is given by the total distance covered divided by total speed. So,

$t=\dfrac{1}{5\times 8}+\dfrac{1}{10\times 25}+\dfrac{1-(1/5)-(1/10)}{20}\\\\t=\dfrac{1}{40}+\dfrac{1}{250}+\dfrac{7}{200}\\\\t=0.064\ h$

So, average speed will be :

$v=\dfrac{d}{t}\\\\v=\dfrac{1}{0.064}\\\\v=15.625\ km/h$

So, the average speed of the whole journey is 15.625 km/h.

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