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kevincan
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I would like to know the answer and the way to figure it? Could't figure it, doesn't seem to be as simple as finding the no: of permutations of letters in 'MISSISSIPPI' though!

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Would it be much easier if it were 6 minutes instead of 8?
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from your original sketch, we know that there are 8 streets that we can not take in order to get to Sarah's house within 8 minutes. Please see attached file.

Also, I know that I have to be within the blue lines, but within the blue lines, there are going to be paths that are not going to work since I have to get to Sarah's house with in 8 minutes.

I have counted the number of horizontal lines (1minute) in the attached file, I have only numbered 1,2,3, and 4. But there are a total of 26 horizontal lines and a total of 24 vertical lines.

This totals to 50 possible lines that I can use in groups of 8 (8minute) to get to Sarah's house. I feel so close, yet so far...
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If she wanted a six minute walk she would need to move up (U) twice and right (R) four times
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Isn't the number of ways 448, is it?
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You're right- sorry for the typo! Did it take a long time to solve?

Congratulations!
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thank you

well, now that I remember my combinatoric course ....

pretty tough question
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Isn't the number of ways 448, is it?


if you don't mind, can you please explain your work?
thanks
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We know Lina wants to take an 8 minute walk. So she would have to move 8 'clicks' up or to the right.

There are several ways to do it:

One is move left once, right 5 times, and up once. So if write a word, we get:
LRRRRRUU --> # of permutations = 8!/5!2! = 168

Another way is
Down once, right 4 times, up 3 times, writing it into a word, we get:
DRRRRUUU --> # of permutations = 8!/4!3! = 280

Total number of ways = 168+280 = 448
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We know Lina wants to take an 8 minute walk. So she would have to move 8 'clicks' up, down, to the left or to the right. The net result must be 4 to the right and 2 up.

There are several ways to do it:

One is move left once, right 5 times, and up twice. So if write a word, we get:
LRRRRRUU --> # of permutations = 8!/5!2! = 168

Another way is
Down once, right 4 times, up 3 times, writing it into a word, we get:
DRRRRUUU --> # of permutations = 8!/4!3! = 280

Total number of ways = 168+280 = 448


Excellent, I've made a couple of changes to make your solution the OE!



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