A car travels 30km at a uniform speed of 40 km/h and the next 30km at a uniform speed of 20km/h. Find its average speed.

26.7 km/h

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28.7 km/h

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26.5 km/h

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25.4 km/h

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Solution

The correct option is A
26.7 km/h

Total distance = 30 km + 30 km = 60 km

Time taken to move first 30 km, $t_{1}$ = $\frac{30}{40}$ = $\frac{3}{4}$ h

Time taken to cover next 30 km, $t_{2}$ = $\frac{30}{20}$ = $\frac{3}{2}$ h

Total time taken = $t_{1}$ + $t_{2}$ = $\frac{3}{4}$ + $\frac{3}{2}$ = $\frac{9}{4}$ h

Hence, average speed of the person = $\frac{T o t a l D i s t a n c e}{T o t a l T i m e}$ = $\frac{60 k m}{(\frac{9}{4} h)}$ = 26.7 km/h

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