Question

A car travels 10km distance at a speed of 80km/hr and returns with a speed of 90km/hr. Calculate its average speed for the whole journey.​

Answer 1

Answer:

17km/hr is the average speed

Answer 2

See

Distance covered while going = Distance covered while coming = 10 km

So

$d_{1} = d _{2} = 10$

As

$time = \frac{distance}{speed}$

That is

$t = \frac{d}{s}$

So time taken while going is

$t_{1} = \frac{10}{80} = \frac{1}{8}$

And

Time taken while coming is

$t_{2} = \frac{10}{90} = \frac{1}{9}$

So

As per formula

$v_{avg} = \frac{ d_{1} + d_{2} }{ t_{1} + t_{2}} = \frac{10 + 10}{ \frac{1}{8} + \frac{1}{9} } = \frac{20}{ \frac{17}{72} }$

So

$v_{avg} = 20 \times \frac{72}{17} = 84.7 \: km |hr$

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