# It took David an hour to ride 20 km from his house to the nearest town. He then spent 40 minutes on the return journey. What was his average speed?

The average speed is simply the rate at which the distance travelled by David varies per unit of time.

you can say that David needed

to make the return trip.

More specifically, David will cover

So, you know the average speed for the first trip and the average speed for the return trip, so you can simply take the average of these two values, right? Wrong!

It is absolutely crucial to avoid going

You know that you have

Therefore, you can say that David has an average speed of

I'll leave the answer rounded to two sig figs, but don't forget that your values justify only one significant figure for the answer.

This is why the equation for average speed is given as

In your case, you have

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David's average speed for the entire journey can be calculated by dividing the total distance traveled (40 km, round trip) by the total time taken (1 hour + 40 minutes, converted to hours).

Total distance = 20 km (to town) + 20 km (return journey) = 40 km Total time = 1 hour + 40 minutes = 1 hour + (40/60) hours = 1 + 2/3 hours = 5/3 hours

Average speed = Total distance / Total time Average speed = 40 km / (5/3) hours = 24 km/h

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To find David's average speed, we first calculate the total distance he traveled and then divide it by the total time taken.

David traveled 20 km from his house to the nearest town and then another 20 km on the return journey, making a total distance of 40 km.

The total time taken is 1 hour (for the outward journey) + 40 minutes (for the return journey). Since 40 minutes is ( \frac{40}{60} ) hours, the total time taken is ( 1 + \frac{40}{60} = \frac{3}{2} ) hours.

To find the average speed, we divide the total distance by the total time:

[ \text{Average speed} = \frac{\text{Total distance}}{\text{Total time}} = \frac{40 \text{ km}}{\frac{3}{2} \text{ hours}} = \frac{40 \times 2}{3} = \frac{80}{3} \text{ km/h} ]

So, David's average speed was ( \frac{80}{3} ) kilometers per hour.

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