An electric shuttle travels along a straight 240-mile route from Facility A to Facility B.… — GMAT

An electric shuttle travels along a straight $240$ -mile route from Facility A to Facility B. For the first $120$ miles of the journey, the shuttle travels at a constant average speed of $60$ miles per hour. For the remaining $120$ miles, due to traffic congestion, the shuttle travels at a constant average speed of $30$ miles per hour. What was the average speed of the electric shuttle, in miles per hour, for the entire $240$ -mile trip?

A
36
40Answer
C
42.5
D
45
E
50

Answer

40 miles per hour

To find the average speed over a journey with varying rates, divide total distance by total time. The shuttle covers

120

miles at

60

mph in

2

hours, and

120

miles at

30

mph in

4

hours. The total travel time is

6

hours for a total distance of

240

miles. Dividing

240

miles by

6

hours yields an average speed of

40

miles per hour.

Step-by-Step Solution

Calculate the time spent on the first leg of the trip.

Time for first leg =

\frac{120 \text{ miles}}{60 \text{ mph}} = 2 \text{ hours}

Time is equal to distance divided by speed.

Calculate the time spent on the second leg of the trip.

Time for second leg =

\frac{120 \text{ miles}}{30 \text{ mph}} = 4 \text{ hours}

Time is equal to distance divided by speed.

Calculate the total time for the entire journey.

Total time =

2 \text{ hours} + 4 \text{ hours} = 6 \text{ hours}

The total duration is the sum of the time spent on each leg.

Compute the overall average speed using total distance divided by total time.

Average speed =

\frac{240 \text{ miles}}{6 \text{ hours}} = 40 \text{ miles per hour}

Average speed is defined as total distance divided by total elapsed time.

Key Concept

Average Speed for a Multi-Leg Trip

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