Practice Test Discussion

Mr Venu travles by car and covers 25% of his journey with a speed of 10 km/hr, 45% of his journey with a speed of 5 km/hr and remaining 30 % of his journey with a speed of 15 km/hr. What will be the average speed of Mr Venu for the whole journey ?

7.40 km/hr

56 km/hr

4.32 km/hr

47 km/hr

None of these

Explanation

Given,

P=25%= $\frac{1}{4}$ , Q=45%= $\frac{9}{20}$ , R= 30%= $\frac{30}{100} = \frac{3}{10}$

X= 10 km/h, Y= 5 km/, Z= 15 km/h

∴ Required average speed= $\frac{1}{\frac{P}{X} + \frac{Q}{Y} + \frac{R}{Z}}$

$= \frac{1}{\frac{1}{4 \times 10} + \frac{9}{20 \times 5} + \frac{3}{10 \times 15}} = \frac{1}{\frac{1}{40} + \frac{9}{100} + \frac{1}{50}} = \frac{1}{\frac{5 + 18 + 4}{200}} = \frac{200}{27}$

= 7.40 km/hr

Hence, Option A is correct.

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