# Math Help - probability

1. ## probability

(n ) = 210 , find the value of n, where n ≥ 2.
. 2

sorry the 2 is supposed to be under n inside the bracket , as in n choose 2. or nC2.

i have no idea how to do this i got it for homework despite the fact that we never did it in class.

2. ## Re: probability

Originally Posted by amyl95
(n ) = 210 , find the value of n, where n ≥ 2.
. 2 sorry the 2 is supposed to be under n inside the bracket , as in n choose 2. or nC2.
i have no idea how to do this i got it for homework despite the fact that we never did it in class.
Can you solve $\frac{n(n-1)}{2}=210$ for $n~?$

3. ## Re: probability

ya then i get n=-20 or n=21, so that must mean that n=21 if it in the question it states that n ≥ 2. thanks but i just don't get where you got n(n-1)/2 ?

4. ## Re: probability

Amy 195

Pls study the formula of combinations. the formula that gives you how many combinations you will get if you have n -distict objects and you combine them by 2 is the one that Plato gave you...