Answer:C
Explanation:
Given
Total distance covered by car [tex]d=12\ miles[/tex]
First it travels [tex]d_1=6\ miles[/tex] with [tex]v_1=30\ mph[/tex]
then it travels [tex]d_2=6\ miles[/tex] with [tex]v_2=60\ mph[/tex]
time taken during first half [tex]t_1=\frac{d_1}{v_1}=\frac{6}{30}=0.2\ hr[/tex]
time taken during Second half [tex]t_1=\frac{d_2}{v_2}=\frac{6}{60}=0.1\ hr[/tex]
average speed [tex]v_{avg}=\frac{distance}{time}[/tex]
[tex]v_{avg}=\frac{12}{0.2+0.1}=\frac{12}{0.3}=40\ mph[/tex]
