Question 421111: There are 10 points A, B, C, …in a plane, no three on the same line. i) How many triangles are determined by these points? ii) How many of these triangles contain the point A?
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! There are 10 points A, B, C, …in a plane, no three on the same line.
i) How many triangles are determined by these points?
3 non-collinear points determine a triangle.
# of triangles = 10C3 = (10*9*8)/(1*2*3) = 120
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ii) How many of these triangles contain the point A?
A plus 2 more points determine a triangle.
# of triangles = 9C2 = (9*8)/(1*2) = 36
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Cheers,
Stan H.
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