Math question? (Official ACT question)

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1

<p>How do I solve this math question…
“Minh Cuts a board in the shape of a regular hexagon and pounds in a nail at an equal distance from each vertex, as shown in the figure below. How many rubber bands will she need in order to stretch a different rubber band across every possible pair of nails?”
Btw This is in a question in the 2007-2008 Practice booklet </p>

<p>([Internet</a> Archive Wayback Machine](<a href=“Wayback Machine”>Wayback Machine)) Its under the 2007 column Question 27.</p>

<p>A. 15
B. 14
C. 12
D. 9
E. 6</p>

2

<p>Is the answer 15?</p>

<p>There are 6 possible nails. Each time you stretch a rubber band, you use 2 nails.</p>

<p>So do</p>

<p>6 nCr 2 on the calculator = 15</p>

3

<p>Ya thats the answer. for some reason i though i was supposed to do 6 c 5…</p>

4

what does nCr2 stand for