Question

David drives half the distance from $A$ to $B$ at $40$ miles per hour and the other half of the distance at $60$ miles per hour. Calculate her average rate of speed, in miles per hour, for the entire trip.

• A. 48
• B. 49
• C. 50
• D. 51
• E. 52

Answer 1

The correct option is A 48

Let the total distance be $x$
Time taken to travel first half distance is $\frac{\frac{x}{2}}{40}=\frac{x}{80}$
Time taken to travel second half distance is $\frac{\frac{x}{2}}{60}=\frac{x}{120}$
Average speed is $\frac{x}{\frac{x}{80}+\frac{x}{120}}=\frac{240}{5}=48$