You are Here: Home >< Maths

# Decision 1 Help please watch

1. Hi, need some help on the following questions:

a)i) Use Dijkstra's algorithm to find the shortest distance from A to J
I did that with no problems, answer was 27 miles

ii) A new road is built connecting F to I. The length of this road is x miles, where x is an integer. A shorter route from A to J than that in part bi) is now available. Find the maximum value of x (2 marks)

And one more question:

a) List the routes, and their lengths, from B to E, in terms of x where appropriate.

BAE = 13 mins
BE = 2x-1 mins
BCDE = 11 + x mins

b) On a particular day, it is known that x = 10

Find the length of an optimal Chinese Postman route on this day, state a possible route corresponding to this minimum length.

I got BAEDCBEB = 72 mins

c) Find, no matter what the value of x, which of the three routes should not be used if the total length of a Chinese Postman route is to be optimal. (5 marks)

Thanks
2. *bump*
3. Well, what have you tried so far?
4. (Original post by ElMoro)
Well, what have you tried so far?
For the first one i know x < 27, but i don't know how to figure it out, for the second one i have no clue
5. *bump*
6. (Original post by EternalDoom)
...
Just worked through the first question.

Got 26 miles for a(i). Used route ADCFGHJ. Have checked twice but my diagram is messy so could be wrong.

For a(ii) my "permanent label" at F is 15C, so using the new edge, FI:
15+x+5<26
20+x<26
x<6

Hope that helps a little. Not sure if I have time to look through the second question.
7. (Original post by ecraven)
For a(ii) my "permanent label" at F is 15C, so using the new edge, FI:
15+x+5<26
20+x<26
x<6
Alternatively, you can do this.

Assume that somehow we end up at F (because we're using the line FI) so the shortest way from F to J using FI (which is FIJ and has length x+5) must be shorter than the way without using FI (which is FGHJ which has length 1+6+4=11)
So, x+5<11
x<6

It's essentially the same as what ecraven has done but I thought I'd mention anyway.

Will get back to you on the second one when I have time.
8. Thanks a bunch, i understand it now, sounds kinda simple now that you think about it, and lemme know when you guys have figured out how to do the second one, and thanks again
9. *bump* any tips on the last question? D:
10. (Original post by EternalDoom)
*bump* any tips on the last question? D:
Sorry, I haven't looked at it yet. I've been quite busy and haven't done D1 in a while but I will get back to you when I can.
11. (Original post by ElMoro)
Sorry, I haven't looked at it yet. I've been quite busy and haven't done D1 in a while but I will get back to you when I can.
okies

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: March 28, 2011
Today on TSR

### Life lessons uni will teach you

Questionable decision-making and constant surprises

### University open days

1. Loughborough University
Fri, 21 Sep '18
2. University of Cambridge
Fri, 21 Sep '18
3. Richmond, The American International University in London
Fri, 21 Sep '18
Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams