Average

What is the average speed of the car, where half of the distance covered passed at speed 66 km/h and the other half at 86 km/h.

Correct result:

v =  74.68 km/h

Solution:

t=s2v1+s2v2  v=st=ss2v1+s2v2  v=2v1v2v1+v2 v=2⋅66⋅8666+86=74.68 km/ht = \dfrac{s}{2v_1}+\dfrac{s}{2v_2} \ \\ \ \\ v = \dfrac{s}{t} = \dfrac{s}{\dfrac{s}{2v_1}+\dfrac{s}{2v_2}} \ \\ \ \\ v = \dfrac{2v_1v_2}{v_1+v_2} \ \\ v = \dfrac{2 \cdot 66 \cdot 86 }{ 66+86} = 74.68 \ \text{km/h}

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