Practice Test Discussion

A person covers 20 km distance with a speed of 5 km/hr, then he covers the next 15 km with a speed of 3 km/hr and the last 10 km is covered by him with a speed of 2 km/hr. Find out the average speed for the whole journey?

$14 \frac{2}{3} km / hr$

$3 \frac{3}{14} km / hr$

$6 \frac{3}{4} km / hr$

175 km/hr

None of these

Explanation

Given,

P=20 km, Q=15 km, R= 10km

X= 5km/h, Y= 3km, Z= 2km/h

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

$= \frac{20 + 15 + 10}{\frac{20}{5} + \frac{15}{3} + \frac{10}{2}} = \frac{45}{4 + 5 + 5} = \frac{45}{14} = 3 \frac{3}{14} km / h$

Hence, Option B is correct.

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