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Bunuel
Pavel has to visit his aunt, who lives exactly eight blocks north and six blocks east of his current location. If Pavel travels only along streets and does not travel diagonally, the shortest possible route connecting the two points is exactly 14 blocks. How many different 14-block routes may Pavel take to travel the shortest possible distance to his aunt’s house?

A. 14
B. (14!)/(8!6!)
C. (22!)/(14!8!)
D. 8!6!
E. 14!8!6!

This problem boils down to an arrangement problem. There are various ways in which you can cover 8 North blocks and 6 East blocks. Go North one block, then East one block, then North 2 blocks, then East 1 block, then North 2 blocks etc
You can represent the ways like this:
NENNENNEEEENNN
NNNNNNNNEEEEEE
NENENENENENENN
and so on...

The number of ways of arranging total 14 letters where 8 are of the same kind and another 6 of the same kind = 14!/(8!*6!)
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Please Bunuel.
It is permutation not combination ?
I mean order matter or not ?
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Given: Pavel has to visit his aunt, who lives exactly eight blocks north and six blocks east of his current location. If Pavel travels only along streets and does not travel diagonally, the shortest possible route connecting the two points is exactly 14 blocks.
Asked: How many different 14-block routes may Pavel take to travel the shortest possible distance to his aunt’s house?

Let us consider the path followed by Pavel as a string consisting 8Ns & 6Es
For example NNNNNNNNEEEEEE

Number of ways of forming the string = 14!/8!6!

IMO B
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Bunuel
Pavel has to visit his aunt, who lives exactly eight blocks north and six blocks east of his current location. If Pavel travels only along streets and does not travel diagonally, the shortest possible route connecting the two points is exactly 14 blocks. How many different 14-block routes may Pavel take to travel the shortest possible distance to his aunt’s house?

A. 14
B. (14!)/(8!6!)
C. (22!)/(14!8!)
D. 8!6!
E. 14!8!6!



Solution:

Let N be a “north” block (i.e., when Pavel travels north) and E be an “east” block (i.e., when he travels east). Thus, one path Pavel can go to his aunt’s house is NNNNNNNNEEEEEE and the total number of paths is 14! / (8!6!) (i.e., the number of ways one can arrange 8 N’s and 6 E’s in NNNNNNNNEEEEEE).

Answer: B
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Bunuel
Pavel has to visit his aunt, who lives exactly eight blocks north and six blocks east of his current location. If Pavel travels only along streets and does not travel diagonally, the shortest possible route connecting the two points is exactly 14 blocks. How many different 14-block routes may Pavel take to travel the shortest possible distance to his aunt’s house?

A. 14
B. (14!)/(8!6!)
C. (22!)/(14!8!)
D. 8!6!
E. 14!8!6!
Kudos for a correct solution.
Here's one more approach.

As is already mentioned above, Pavel's route will consist of 14 steps (Norths and Easts).
6 of those steps will be Easts and the rest will be Norths.

So, let's select the 6 steps that will be Easts and let the rest be Norths.

In how many ways can we select 6 of the 14 steps?
Well, since the order in which we select the steps does not matter, we can use combinations.
So, we can select the 6 steps in 14C6 ways.
14C6 = 14!/(8!6!)

Answer: B

IMPORTANT: Notice that I said the order in which we select the steps does not matter. In other words, selecting steps 2, 4, 5, 8, 10, and 13 to be Easts is the same as selecting steps 4, 5, 10, 8, 13 and 2. Given this, we can use combinations.

Cheers,
Brent
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