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 answer:

v =  74.68 km/h

Step-by-step explanation:

$$\begin{gathered} t={\displaystyle \frac{s}{2v_1}}+{\displaystyle \frac{s}{2v_2}} \\ v={\displaystyle \frac{s}{t}}={\displaystyle \frac{s}{{\displaystyle \frac{s}{2v_1}}+{\displaystyle \frac{s}{2v_2}}}} \\ v={\displaystyle \frac{2v_1{v}_2}{v_1+v_2}} \\ v={\displaystyle \frac{2\cdot 66\cdot 86}{66+86}}=74.68\text{ km/h} \end{gathered}$$

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