I need help with this problem

[Nicolita]

I need to write a problem using the following elements.
1. Travel by air from Memphis, TN, to Las Vegas, NV, with stops in Oklahoma City, OK, and El Paso, TX en route.
2. Students have a map of the United States that shows cities and a distance scale in kilometers.
3. Require use of straight-line distance in kilometers for each leg of the trip.
4. Average aircraft groundspeed is 380km/hour from Memphis to Oklahoma CIty and 310km/hour from Oklahoma CIty to Las Vegas.

This is what I wrote, but is wrong.

Lisa has to travel by air from Memphis, TN to Las Vegas, NV with stops in Oklahoma City, OK ad EL Paso, TX en route. The distance between Memphis to Oklahoma is 757km, from OK to El Paso is 1088km, and from El Paso to Las Vegas is 1177km. The average aircraft groundspeed is 380km/hour from Memphis to Oklahoma City and 310 km/hour from Oklahoma City to Las Vegas. Find the average ground speed for the journey.

I also need to write the process that use to construct the problem, and this is what I wrote. The speeds at different parts of the journey are given so we can ask to find the average ground speed. We have to provide the distance between different points.

I also need to write the steps students should follow to resolve the problem.
1. Calculate times for different parts of journey; each distance divided by speed for that region
2. Calculate total time. Add all the times
3. Find the total distance. Add all the distances
4. Find the average ground speed.

The answer I get is 302km, which is wrong.

Comments from the teacher:

Problem is missing an element
Is the ground speed an appropriate thing to have students find?
Missing some students steps needed for the solution
Wrong answer to the problem.

Thank You so much for your help.

 

[Denis]

I need to write a problem using the following elements.
1. Travel by air from Memphis, TN, to Las Vegas, NV, with stops in Oklahoma City, OK, and El Paso, TX en route.
2. Students have a map of the United States that shows cities and a distance scale in kilometers.
3. Require use of straight-line distance in kilometers for each leg of the trip.
4. Average aircraft groundspeed is 380km/hour from Memphis to Oklahoma CIty and 310km/hour from Oklahoma CIty to Las Vegas.
This is what I wrote, but is wrong.

Lisa has to travel by air from Memphis, TN to Las Vegas, NV with stops in Oklahoma City, OK ad EL Paso, TX en route. The distance between Memphis to Oklahoma is 757km, from OK to El Paso is 1088km, and from El Paso to Las Vegas is 1177km. The average aircraft groundspeed is 380km/hour from Memphis to Oklahoma City and 310 km/hour from Oklahoma City to Las Vegas. Find the average ground speed for the journey.

I also need to write the process that use to construct the problem, and this is what I wrote. The speeds at different parts of the journey are given so we can ask to find the average ground speed. We have to provide the distance between different points.

I also need to write the steps students should follow to resolve the problem.
1. Calculate times for different parts of journey; each distance divided by speed for that region
2. Calculate total time. Add all the times
3. Find the total distance. Add all the distances
4. Find the average ground speed.
The answer I get is 302km, which is wrong.
Comments from the teacher:
Problem is missing an element
Is the ground speed an appropriate thing to have students find?
Missing some students steps needed for the solution
Wrong answer to the problem. Thank You so much for your help.

Boy oh boy oh boy oh boy...
Can a teacher complicate something easy more than this?!

Formula: speed = distance divided by time

You have 2 instances:
1: 757 miles at speed of 380: time = 757/380
2: 1088+1177 = 2265 miles at speed of 310: time = 2265/310

add the times: t = 757/380 + 2265/310
add the distances: d = 757 + 2265

Average speed = d/t : that'll give you very close to 325

 

[Gene]

757/380 = 2 hrs
1088/310 = 3.5 hrs
1177/310 = 3.8 hrs
-----------------
3022/325 = 9.3 hrs
I don't know how accurate your distances are expected to be but
http://www.indo.com/distance/
gives 684, 919 and 994 respectively.

Comments from the teacher:
Problem is missing an element
Maybe the split of OK-TX-NV legs? I would say what you wrote should be okay if that is it. Or should they have to FIND the distances since they have the map?

Is the ground speed an appropriate thing to have students find?
As appropriate as most problems.

Missing some students steps needed for the solution
See the first comment.

Wrong answer to the problem.
Finally one I agree with.