Morwen bikes around his neighborhood for an hour. He averages 15 mph for the first 40 minutes, but then he tires and averages 10 mph for the last 20 minutes. What is is his average speed for the whole hour?

Very much like your other problem

total distance = 15(40/60) + 10(20/60) = 10+10/3 = 40/3 miles in one hour = 13.3 miles per hour

Solve for z in the following proportion:

z : 14 :: z − 3 : 8

To find Morwen's average speed for the whole hour, we need to calculate the total distance he traveled and divide it by the total time taken.

First, we need to convert the time into hours. Morwen rode for 40 minutes, which is 40/60 = 2/3 hours. He also rode for 20 minutes, which is 20/60 = 1/3 hours.

Next, we can calculate the total distance traveled. To do this, we calculate the distance traveled during the first 40 minutes and add it to the distance traveled during the last 20 minutes.

Distance traveled in first 40 minutes = speed × time = 15 mph × (2/3) hours = 10 miles.
Distance traveled in last 20 minutes = speed × time = 10 mph × (1/3) hours = 10/3 miles.

Total distance = distance traveled in first 40 minutes + distance traveled in last 20 minutes = 10 miles + (10/3) miles = 40/3 miles.

Now, we can calculate the average speed by dividing the total distance by the total time taken:

Average speed = Total distance ÷ Total time = (40/3) miles ÷ 1 hour = 40/3 mph.

Therefore, Morwen's average speed for the whole hour is approximately 13.33 mph.