Question 73

A girl goes from M to N at a speed of 25 km/h and returns to M at a speed of 37.5 km/h, via the same route. What is the girl's average speed (in km/h)?

Solution

average speed = $$\frac{2\times\ speed\ while\ going\times\ speed\ while\ returning}{speed\ while\ going\ +\ speed\ while\ returning}$$

= $$\frac{2\times\ 25\times\ 37.5}{25+37.5}$$

= $$\frac{2\times\ 25\times\ 37.5}{62.5}$$

= $$2\times15$$

= 30 km/h

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