Reference
Probability
Probabilities are never greater than 1 or less than 0.Complement:

P(A and B) = P(A)•P(B)
For AND, multiply individual probabilities.  Check for replacement.

P(A or B) = P(A)+P(B)-P(A and B)
For OR, add the individual probabilities and subtract the overlap.

Factorial:
n! = n(n-1)(n-2)(n-3)…1
Similar Triangles
 Two triangles are similar if the corresponding angles are congruent and the corresponding sides are in proportion.

Additional method of solution:  A line  parallel to one side of a triangle divides the non-parallel sides proportionally.

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