Answer:
The correct option is B.
Step-by-step explanation:
It is given that Susan drove an average speed of 30 miles per hour for the first 30 miles of a trip & then at a average speed of 60 miles/hr for the remaining 30 miles of the trip.
[tex]Time=\frac{Distance}{Speed}[/tex]
Time taken by Susan in first 30 miles is
[tex]T_1=\frac{30}{30}=1[/tex]
Time taken by Susan in remaining 30 miles is
[tex]T_2=\frac{30}{60}=0.5[/tex]
Total distance covered by Susan is
[tex]D=30+30=60[/tex]
Total time taken by susan to complete 60 miles trip is
[tex]T=T_1+T_2[/tex]
[tex]T=1+0.5=1.5[/tex]
Susan's avg speed in miles/hr for the entire trip is
[tex]S=\frac{60}{1.5}=40[/tex]
The average speed of susan for entire trip is 40. Therefore the correct option is B.
