Finding average speed & distance traveled?

[Luxurious]

Homework Statement

Sally travels by car from one city to another. She drives for 30.0 min at 52.0 km/h, 35.0 min at 48.0 km/h, and 23.0 min at 50.0 km/h, and she spends 10.0 min eating lunch and buying gas.

Homework Equations

avg. speed= distance traveled / time of travel

The Attempt at a Solution

first, I added all three speeds (52+48+50) and divided by 3. I got 50 as the average speed, but the website says I'm incorrect.

How can I find the average speed without the distance traveled?

avg. speed = distance traveled / (30+35+23)
avg. speed = distance traveled / 88

 

[Delphi51]

I don't think you can find the average speed without first finding the distance!
It shouldn't be hard to work out the distances - just use d = vt for each. Get the total distance and the total time, then use the "relevant equation".

 

[tomcue]

min

To find the distance traveled, we can use the formula:
distance = speed x time

For the first leg of the trip, Sally traveled for 30 min at 52 km/h, so the distance traveled is:
distance = 52 km/h x 30 min = 1560 km

For the second leg of the trip, Sally traveled for 35 min at 48 km/h, so the distance traveled is:
distance = 48 km/h x 35 min = 1680 km

For the third leg of the trip, Sally traveled for 23 min at 50 km/h, so the distance traveled is:
distance = 50 km/h x 23 min = 1150 km

Now, we can add all three distances together to get the total distance traveled:
total distance = 1560 km + 1680 km + 1150 km = 4390 km

Plugging this into our equation for average speed, we get:
avg. speed = 4390 km / 88 min = 49.77 km/h

Therefore, the average speed for Sally's trip is 49.77 km/h.