Question

I have No clue how to do this problem can someone help please
. Evaluate 9C5
126
24
3024
120

Answer 1

9.8.7.6.5
--------
5.4.3.2.1

Answer 2

mine just cuts off the 4! and leaves the rest

Answer 3

so take 9*8*7*6*5= 15120
and 5*4*3*2*1= 120
so the answer would be 120?

Answer 4

Like amistre64 said, he left out the 4!, so divide your answer by 4!.

Answer 5

3780 is answer

Answer 6

\[\frac{9\times8\times7\times6}{4\times3\times2\times1}=126\]

Answer 7

Ohhh wait that wouldn't give you an answer within the choices... oops

Answer 8

Zarkon's looks correct

Answer 9

\[nCr = \frac{n\!!}{r\!!(n-r)\!!}\]
\[\implies 9C5 = \frac{9\!!}{5\!!(9-5)\!!} = \frac{9\!!}{5\!! 4\!!} = \frac{362880}{120 \cdot 24} = 126\]

Answer 10

Although typically you would not multiply everything out until after canceling numbers in the top and bottom.

Answer 11

\[9 C 5=\frac{9\times 8\times 7\times 6\times 5}{4\times 3\times 2}=9\times 2\times 7=126\]

Answer 12

Phi has a point, it's a lot easier (and neater) to evaluate when you cancel out a few numbers.

Answer 13

cancel first multiply last because "the number of ways to choose k from a set of n" is always in integer

Answer 14

actually there is a typo in the middle part of my answer

Answer 15

5 shouldn't be there.

Answer 16

thank you for showing me how to do this problem :)

Answer 17

9.8.7.6.5
--------
5.4.3.2.1

9.8.7.6
--------
4.3.2

9.2.7.6
--------
3.2

9.2.7.2
--------
2

9.2.7 = 63.2 = 126