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A car travels 100 km at a speed of 60 km/h and returns with a speed of 40 km/h. Calculate the average speed for the whole journey.
For the first journey
Distance traveled $=100\ km$
Speed $60\ km/h$
Therefore, Time taken for the journey $t_1=\frac{distance}{time}$
$=\frac{100}{60}$
$=\frac{5}{3}\ h$
For Retuning journey:
Distance travelled $=100\ km$
Speed $=40\ m/s$
Therefore, time taken for the returning $t_2=\frac{distance}{time}$
$=\frac{100}{40}$
$=\frac{5}{2}\ h$
Therefore, Average speed of the car $=\frac{Total\ distance}{Total\ time}$
$=\frac{100+100}{\frac{5}{3}+\frac{5}{2}}$
$=\frac{200}{\frac{10+15}{6}}$
$=\frac{200}{\frac{25}{6}}$
$=\frac{200\times6}{25}$
$=48\ km/h$
Thus, the average speed for the whole journey.
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