Question

nC4=70 calculate n?

Answer 1

n = 8

Answer 2

explain plzzzzzz

Answer 3

\[\dbinom{8}{4}=\frac{8\times 7\times 6\times 5}{4\times 3\times 2}=2\times 7\times 5 = 70\]

Answer 4

i guess if you want a method i did not really use one. i know
\[\frac{10}{4}\] is large (210) so i just tried 8 and it worked

Answer 5

any generic method. this u did as u kno answer is 8..........

ohhh got hw the way u think..

Answer 6

yea i just guessed and got it on the first try. if you write

\[\frac{n!}{4!\times (n-4)!}=70\] i think this would be a pain to solve using algebra.

Answer 7

I did but was not able to solve equation dear..

Answer 8

ya anyway fine

Answer 9

nC4 = nP4/4! = 70

nP4 = 70(4!)

n*(n-1)*(n-2)*(n-3) = 1680

(n^2 -n)(n^2 -5n+6) = 1680

n^2 -5n +6
n^2 -n
--------------
n^4 -5n^3 +6n^2
-n^3 +5n^2 -6n
---------------------
n^4 -6n^3 +11n^2 -6n = 1680

n^4 -6n^3 +11n^2 -6n -1680= 0

We can hash out the details, but when you graph it this has roots
at -5 and 8; since -5 is prolly outside our scope of interest; n=8