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