Average speed 4

Starting at home, Tony traveled uphill to the store for 45 minutes at 8 miles per hour. he then traveled back home on the same path at a speed of 24 miles per hour. What is his average speed for the entire trip?

Correct answer:

v =  12 mph

Step-by-step explanation:

$$\begin{gathered} t_1=45/60=\frac{3}{4}=0.75\text{h} \\ {v}_1=8\text{mph} \\ {v}_2=24\text{mph} \\ s=v_1\cdot t_1=8\cdot 0.75=6\text{km} \\ {t}_2=s/v_2=6/24=\frac{1}{4}=0.25\text{h} \\ v=2\cdot s/(t_1+t_2)=2\cdot 6/(0.75+0.25)=12\text{mph} \end{gathered}$$

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