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Fran the fly starts at (0,0) and each minute moves one unit right or one unit up. She is trying to get to the point (5,7). However, at (4,3) there is a spider that will eat her if she goes through that point. In how many ways can Fran reach (5,7)?

 Feb 10, 2020
 #1
avatar+557 
+2

Well, I don't really know this but I'll give it a shot:

 

We need to caculate the amount of ways from (0,0) to (5,7): 12C5=792 ways from (0,0) to (5,7), and then subtract that by the amount of ways that pass the spider.

 

Next, we also need to caculate the paths from (0,0) to (4,3) and multiply that by the amount of paths from (4,3) to (5,7):

 

7C3 * 5C1 = 175.

 

792 - 175 = 617.

 Feb 10, 2020
 #2
avatar+111389 
+1

That seems correct, AnimalMaster......I'm giving it a "thumbs-up"

 

 

cool cool cool

CPhill  Feb 10, 2020
 #3
avatar+557 
+1

Thank you CPhill!

AnimalMaster  Feb 10, 2020
 #4
avatar
+1

617 was correct! Thank you both and have a good day :D

 Feb 10, 2020

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