Here is 15 dots. if you select 3 dots randomly, what is the probability that 3 dots make a triangle?
a. 440/455
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The picture of 15 dots is missing.
See the enclosed pictures.
Answer is = (15C3 - 3 × 5C3 - 5 - 2 × 3 - 2) / 15C3
= 412/455
15C3 = ways of selecting 3 vertices.
5C3 = number of ways of selecting 3 points from one row.
5 = number of columns
3 + 3 + 2 are inclined diagonals.
See the enclosed pictures.
Answer is = (15C3 - 3 × 5C3 - 5 - 2 × 3 - 2) / 15C3
= 412/455
15C3 = ways of selecting 3 vertices.
5C3 = number of ways of selecting 3 points from one row.
5 = number of columns
3 + 3 + 2 are inclined diagonals.
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kvnmurty:
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