# how many ways

• July 6th 2006, 02:18 PM
Judi
how many ways
The figure shows all roads between Q(Quarryton), R(Richfield), and B(Bayview). Martina is traveling from Quarryton to Bayview and back. How many different ways could she make the round-trip, going through Richfield exactly once on a round-trip and not traveling any section of road more than once on a round trip? The ans is 12. But I don't 12~
• July 6th 2006, 02:27 PM
Quick
I just want to say your skills at paint are somewhat terrifying. But getting on subject...

a nice way to do this is tree diagrams...

first draw all the combinations when going from Q to B to R back to Q
Code:

            Q           /         R--- Q         /  \       /    Q Q-----B       \    Q         \  /         R---Q           \             Q
So there are 6 combinations that way

Now draw the number of combinations from Q to R to B back to Q
Code:

      B---Q     /     R---B---Q   /    B---Q   /    / Q-----R   \    \   \    B---Q     R---B---Q     \       B---Q
There are 6 combinations this way...

altogether that makes 12
• July 6th 2006, 04:27 PM
Soroban
Nice diagrams and great explanation, Quick!

I sort of "eyeballed" the diagram and reasoned it out.

Under the restrictions of the problem,
. . there are only two routes that Martina can take.

$[1]\;\;Q\quad\longrightarrow\quad B\quad\longrightarrow\quad R \quad\longrightarrow\quad Q$
. . . . .1 way . . .2 ways . . .3 ways . . . . $1 \times 2 \times 3 \:=\:6\;ways$

$[2]\;\;Q\quad\longrightarrow\quad R\quad\longrightarrow\quad B\quad\longrightarrow\quad Q$
. . . . 3 ways . . .2 ways . . .1 way . . . . $3 \times 2 \times 1 \:=\:6\;ways$

Therefore, there are: . $6 + 6 \:=\:12$ ways.

But your tree diagrams are great: . $\text{1 picture} \;= \;1\text{ kiloword}$

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

$FYI$

1 millihelen = amount of beauty required to launch one ship.

• July 6th 2006, 04:47 PM
Quick
Quote:

Originally Posted by Soroban
Nice diagrams and great explanation, Quick!

Thank you, I learned how to do those code things from you! Although I can't imagine trying to make geometric shapes out of them. You know, I had such a picky 8th grade teacher that she would have pointed out that the diagrams didn't go upward :rolleyes:
• July 6th 2006, 06:02 PM
Judi
Thanks, and I will work on the drawing
• July 6th 2006, 06:13 PM
ThePerfectHacker
Quote:

Originally Posted by Soroban
Nice diagrams and great explanation, Quick!

I must admit I wish I had those art coding skills, they clearly come in useful. O' Alas, the great Lord did not bless me with art :(
• July 6th 2006, 06:56 PM
c_323_h
Quote:

Originally Posted by Soroban
$\text{1 picture} \;= \;1\text{ kiloword}$

haha...i like that.