Question 891547
Ralph knows that there are 15 distinguishable possibilities when 2 people are chosen to form a committee from a particular group of N people.
A) describe what values if N would be admissible in this problem.
<pre>
{{{X(X-1)/2!}}}{{{""=""}}}{{{15}}}
{{{X(X-1)}}}{{{""=""}}}{{{2*15}}}
{{{X^2-X}}}{{{""=""}}}{{{30}}}
{{{X^2-X-30}}}{{{""=""}}}{{{"0"}}}
{{{(X-6)(X+5)}}}{{{""=""}}}{{{"0"}}}

{{{X-6=0}}},  {{{X+5=0}}}
{{{X=6}}},    {{{cross(X=-5)}}}

So the number to pick 2 from in order to have 15 distinguishable possibilities
is 6.

Every time we pick 2 from the 6, we leave 4 behind. So there are also
15 ways to choose 4.  C(6,2) = C(6,4) = 15

So the admissible numbers we could pick 15 ways from the 6 are 2 and 4. 
</pre>
B) Determine the number of people in the larger group, N
<pre>
Isn't it just asking for the larger group of 4?  (Am I missing something?)

Edwin</pre>