Club Membership

[medea66]

Is this a perm/comb?

[anshul265]

Permutation.

nC2 = 190
n!
------- = 190
n-2! 2!

n (n-1)
-------- = 190
2

n^2 - n = 380

n^2 - n - 380 = 0

n = 20, 18.

[pre-gmat]

How did u get this part?

n (n-1)
-------- = 190
2

[kuroneko1313]

How did u get this part?

n (n-1)
-------- = 190
2

Consider this:

n! = n (n-1) (n-2)!

As posted by anshul265:

n!
------- = 190
n-2! 2!

n (n-1) (n-2)!
----------------- = 190
n-2! 2!

now the (n-2)! gets canceled out by the denominator, leaving only n (n-1) at the top. Hope that helps.

[raju232007]

there are 190 possible selections to select 2 people from n members

so nC2=190

i.e n!/2!((n-2)!=190
n!=380(n-2)!

w.k.t n!=n*(n-1)*(n-2)!


n*(n-1)*(n-2)!=380(n-2)!

n(n-1)=380

Solving this we get n=20

[vishubn]

i plugged in numbers

ANd got the answer with

nC2=190

where n is the number of people wanting to be filled for two slots !

20 possiblity for the first slot and 19 for the second !
as it says differnt number of ways its combi

20*19/2*1 = 10* 19=190

Vishu

[medea66]

Okay, so at the end you have n^2-n-380 and then you factor this out to get 20????