Calling all Math Nerds

Here's a problem that is a real life question I'd like to solve. I don't know if you could do this using ColdFusion (I know you don't need to), but if you do use CF, you get extra credit. :)

My wife and I have argued about which of two possible routes home is the quickest, and I figured some of the Math geniuses out there would be able to quickly solve this. The diagram below represents a part of my normal daily travels. I want to get from point A to C. I have the choice of taking the A->B->C route, or the A->D->C route. As you can see, all for sides of the square are 1/2 mile. Let's also assume that I always start from a complete stop at point A, regardless of which route I choose, and I have to come to a complete stop at the end (point C), regardless of which route I choose.

Math Diagram

The tricky part is that there are varying speed limits. The first route (shown in red):

  1. A->B = 40 mph.
  2. No stop sign at B.
  3. B->C = 25 mph.
Let's assume that I can take the B corner at 8 miles an hour (no stop sign, and assuming that there are no cars coming that I'd have to stop for before making the turn).

The second route (shown in blue):

  1. A->D = 30 mph.
  2. Stop sign at D.
  3. D->C = 30 mph.

Assuming I didn't miss any assumptions, which route of the two would be fastest?

Comments
Not sure you need to bother with a math nerd.
The average speed on the red route is higher, and has no stops.
# Posted By Tom Chiverton | 2/16/09 12:49 AM
The starting and stopping stuff is just a needless complication. Your acceleration factor can't be known and just doesn't matter for this problem.

At 45mph, 1 mile takes 90 seconds
At 30mph, 1 mile takes 120 seconds
At 25mph, 1 mile takes 144 seconds

AB + BC route = 117 seconds
Blue route = 120 seconds

The red route is shorter even before you factor in the blue stop.

Even if the acceleration factor is thrown in and makes any appreciable difference (it may decrease the time difference, but there would still be a difference), the red route will be faster.
# Posted By Lyle | 2/16/09 1:15 AM
Lyle,

If I were grading this problem on your math test, you'd get a C. The A+B side is 40 MPH, not 45. :)
# Posted By Jake Munson | 2/16/09 5:01 AM
What is the distance travelled at 8mph.... This is the missing part...
# Posted By Dave | 2/16/09 3:20 PM
Not far...as long as it takes to round a corner. And there is deceleration and acceleration in there as well. :\
# Posted By Jake Munson | 2/16/09 3:24 PM
Get yourself one of these: http://www.newlaunches.com/archives/the_worlds_sma...

and then you can take the A -> C route.
# Posted By Damon Gentry | 2/16/09 5:12 PM
Ha ha...that would be awesome Damon. :)
# Posted By Jake Munson | 2/17/09 10:05 AM
Why don't you measure the time required for several times, and take an average instead? :)

and btw, do you really do a complete stop at a stop sign? :D If not, then the lineup of how many cars at the stop sign means a lot more.
# Posted By Henry Ho | 2/18/09 10:32 AM
Yes, I generally do a complete stop at a stop sign.

I could time it, but I thought it would be a fun problem to throw on my blog. :)
# Posted By Jake Munson | 2/18/09 10:34 AM
The red side.

My question is so which side did you take and which side did your wife take? :)
# Posted By Shannon | 6/27/09 6:35 PM
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