Question

find n if nc5=nc6 and 15cn

Answer 1

Answer:

n=11 and 15cn= 1365

Step-by-step explanation:

nc5=nc6

n!/n-5! . 5! = n!/n-6! . 6! (cancel the n! on both sides )

we get

n-6! . 6!/n-5! . 5! = 1

n-6.  . 6 . 5!/ n-5 . n-6! . 5! = 1

now cut n-6! and 5! , we get

6/n-5=1

6= n-5

n=  6+5

n=11

15c11 = 15!/15-11! . 11!

15!/4!.11! = 15*14*13*12/1*2*3*4 = 1365

Answer 2

Answer:

n=11 ; 15Cn = 1365

Step-by-step explanation:

Here nC5=nC6

[ nCr = nCn-r ]

.•. [ r = 5 ]

=> n - r = 6

=> n = 6 + 5

=> n = 11

.•. 15Cn = ?

=> 15C11 = 15C4

=> 15*14*13*12

1*2*3*4

=> 1365