Expert: Azeem Hussain - 3/1/2009

Question
I am having trouble with this question:
Plot 7 non-collinear points on a page. How many different triangles can be formed by joining three of the points at a time.
I also don't get 'at a time'. What does it mean?
Thank you.

Answer
Hey Mia!

Ignore the "at a time" part.  To make a triangle you need to join three points, and that's all that's saying.

Make 7 random points on a page.  Now make as many different triangles as you can.  There are quite a few.  If you're doing this systematically, you will find yourself drawing the same ones two or three times over.

The correct number may be found by using a statistics procedure.  There are three elements (points to join).  The formula would be (n)(n-1)(n-2)/3, where n is the starting number (7 in this case).

I get 70 triangles using this method.

Thanks for asking,
Azeem