Question

Andy drives 300 miles to Lake Tahoe at 70 miles per hour and returns home at 50 mph. What is his average speed for the round trip. (It is not 6o miles per hour.)

Write expressions for the time it takes for each leg of the trip if Andy drives a distance d, at speed r base 1 and returns at speed r base 2

Answer 1

300/70 is the total time to get out there.
300/50 is the total time to get back.

In variables, distance = 300
speed out = r1
speed back = r2

so you have [(d/r1)+(d/r2)]/2

Answer 2

er, I don't think that's right actually...d/r1 gives the amount of time it takes to go out, d/r2 gives the amount of time it takes to come back.

To find the average, you need the total distance traveled (d*2) divided by the total time it took (d/21+d/r2)

Answer 3

I dont think the total time is right

Answer 4

r u sure its right

Answer 5

u sure

Answer 6

300mi/70mph = 4.286 hours to get there
300mi/50mph = 6.00 hours to get back

Total time traveled = 4.286 + 6.000 = 10.286 hours

Total distance traveled = 300*2 = 600 mi

Average speed = distance/time = 600/10.286 = 58.33mph