Problem Solving

[GMAT math practice question]

Tom travels from A to B at a constant speed of 4 miles per hour and returns from B to A at a constant speed of 8 miles per hour. What is Tom's average speed for the entire journey?

A. 14/3
B. 5
C. 16/3
D. 17/3
E. 18/3

Average speed = Total distance/total time = $$\frac{2x}{\frac{3x}{8}}$$ = 16/3. Hence C

Let x miles be the distance between A & B.
Time taken in reaching from A to B = Dist/speed = x/4
Time taken in reaching from B to A = Dist/speed = x/8
Total distance = x+x=2x
Total time = x/4+x/8 = 3x/8
Avg speed = total dist/total time = 2x/3x/8 = 16/3 miles/hr
Thus ans is C.

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The average speed is calculated by dividing the total distance by the total time. We often encounter this type of question on the GMAT exam.

Let d be the distance between A and B.
The time that Tom takes to travel from A to B is d/4 and the time that he takes to travel from B to A is d/8.
The total time taken is (d/4) + (d/8) = 3d/8.
The average speed is 2d / (3d/8) = 16/3.

Therefore, the answer is C.
Answer: C