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Triton · 2009 October 12th, 06:59 AM

There are 15 points in a plane, of which 6 points are collinear. How many different:

a. Triangles &
b. Straight lines can be drawn.

thanx.

Attack · 2009 October 12th, 08:02 AM

A straight line can be drawn between any 2 points.
We can choose 2 points out of 15 in 15C2 ways.

But 6 points over here are collinear. that is we can draw only one line through them.

So for those 15 points we can draw 15C2- 6C2 + 1 distinct lines.

Similarly we can draw 15C3- 6C3 triangles.

Triton · 2009 October 13th, 06:28 AM

thank you so much......the answers are correct !

2009 October 12th, 06:59 AM	#1 (permalink)
Triton Eager! Join Date: Aug 2004 Location: MN, USA Posts: 83	Combination ! There are 15 points in a plane, of which 6 points are collinear. How many different: a. Triangles & b. Straight lines can be drawn. thanx.

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2009 October 12th, 08:02 AM	#2 (permalink)
Attack Eager! Join Date: Apr 2009 Location: Chicago Posts: 31	A straight line can be drawn between any 2 points. We can choose 2 points out of 15 in 15C2 ways. But 6 points over here are collinear. that is we can draw only one line through them. So for those 15 points we can draw 15C2- 6C2 + 1 distinct lines. Similarly we can draw 15C3- 6C3 triangles.

2009 October 13th, 06:28 AM	#3 (permalink)
Triton Eager! Join Date: Aug 2004 Location: MN, USA Posts: 83	thank you so much......the answers are correct !

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