Bunuel wrote:
If one of two parallel lines has 7 points on it and the other has 8, how many unique triangles can be drawn using the points?
A. 168
B. 196
C. 316
D. 364
E. 455
I would say visualize what is happening.
Imagine one line, which has 7 points and there is only 1 point on the opposite side. How many unique triangles we can make?
7C2 * 1 = 21
Now there are actually 8 points on the other side and not just 1 point.
So we get 21*8=168
Let's go on the other side of the table. Now we have 8 points out of which we have to select 2 and there are 7 points on the opposite side.
We get 8C2*7=28*7=196
Total Unique Triangles = 168+196=364 (Tip: Just add 200 to 168 and then subtract 4)
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