Question

William drove for 5 hours at an average speed of 54 mi/h. For the first two hours, he drove 45 mi/h. What was his average speed for the last three hours?

A. 40 mi/h
B. 50 mi/h
C. 60 mi/h
D. 65 mi/h

Answer 1

Therefore, William's average speed for the last three hours was 60 mi/h, so the answer is (C) 60 mi/h.

Explanation:

We can start by using the formula:

average speed = total distance / total time

We know that William drove for a total of 5 hours at an average speed of 54 mi/h, so the total distance he covered was:

total distance = average speed x total time

total distance = 54 mi/h x 5 h

total distance = 270 miles

We also know that for the first two hours, his speed was 45 mi/h. Therefore, he covered a distance of:

distance for first 2 hours = speed x time

distance for first 2 hours = 45 mi/h x 2 h

distance for first 2 hours = 90 miles

To find out the distance he covered for the last three hours, we can subtract the distance he covered in the first two hours from the total distance:

distance for last 3 hours = total distance - distance for first 2 hours

distance for last 3 hours = 270 miles - 90 miles

distance for last 3 hours = 180 miles

Finally, we can use the formula again to find his average speed for the last three hours:

average speed = distance for last 3 hours / time for last 3 hours

average speed = 180 miles / 3 hours

average speed = 60 mi/h

Answer 2

Given:

William drove for 5 hours at an average speed of 54 mi/h.

For the first two hours, he drove at a speed of 45 mi/h.

To find:

William's average speed for the last three hours.

Solution:

Let
`x` represent the average speed for the last three hours (in mi/h).

The total distance traveled in the first two hours is
`\sf\:45 \, \text{mi/h} * 2 \, \text{h} = 90 \, \text{miles} \\`.

The total distance traveled in 5 hours is
`\sf\:54 \, \text{mi/h} * 5 \, \text{h} = 270 \, \text{miles} \\`.

The distance traveled in the last three hours is
`\sf\:270 \, \text{miles} - 90 \, \text{miles} = 180 \, \text{miles} \\`.

The average speed for the last three hours can be calculated as:

`\sf\:\frac{\text{distance}}{\text{time}} = \frac{180 \, \text{mi}}{3 \, \text{h}} \\`

Simplifying the expression:

`\sf\:(180)/(3) = 60 \, \text{mi/h} \\`

Therefore, the average speed for the last three hours is
`\sf\:\boxed{60 \, \text{mi/h}} \\`.