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# Combinations

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Marvin the fly starts at \$(0,0).\$ Each step, Marvin moves one unit right or one unit up. He is trying to get to the point \$(5,7)\$. However, at \$(4,3)\$ there is a frog that will eat him if he goes through that point. In how many ways can Marvin reach \$(5,7)\$?

This problem is a bit different than the one web2.0calc.

I got 792- something. I can not find what to subtract from, also known as complementary counting btw

May 21, 2020
edited by Guest  May 21, 2020
edited by Guest  May 21, 2020

#1
-1

You subtract C(7,2)*C(5,2), which gives you C(12,5) - C(7,2)*C(5,2) = 582.

May 21, 2020
#2
-1

That is wrong bro

May 21, 2020
#3
+1

Hi Sarvajit,

You're on the right track! What you have to subtract is the number of paths from (0,0) to (5,7) that pass through (4,3). To calculate this, all you have to do it multiply the number of paths from (0,0) to (4,3) by the number of paths from (4,3) to (5,7).

I think you can do the rest!

Tell me if you need any help!

:)

May 21, 2020
#4
-1

OK thanks a lot

May 21, 2020