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counting and probability senior

Problem

Seven sticks with lengths 2, 3, 5, 7, 11, 13 and 17 inches are placed in a box. Three of the sticks are randomly selected. What is the probability that a triangle can be formed by joining the endpoints of the sticks? Express your answer as a common fraction.
Solution
By the triangle inequality, three segments form a triangle if and only if the sum of the smaller two lengths exceeds the greatest length. Therefore, if is one of the sticks drawn, then the three sticks cannot be used to form a triangle. If 3 is the smallest length drawn, then the possible sets of sticks are (3,5,7) and (3,11,13). If 5 is the smallest length drawn, then (5,7,11), (5,11,13), and (5,13,17) are the sets that satisfy the triangle inequality. If 7 is the smallest length drawn, then (7,11,13), (7,11,17), (7,13,17) all satisfy the triangle inequality. Finally, (11,13,17) satisfies the triangle inequality. In total, there are sets of sticks that could be used to form a triangle. There are equally likely sets of 3 sticks, so the probability that one of the 9 sets that form a triangle will be chosen is .
Final answer
\frac{9}{35}