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Printsmc
counting and probability senior
Problem
How many noncongruent integer-sided triangles with positive area and perimeter less than 15 are neither equilateral, isosceles, nor right triangles?
(A)
(B)
(C)
(D)
Solution
Since we want non-congruent triangles that are neither isosceles nor equilateral, we can just list side lengths with . Furthermore, "positive area" tells us that and the perimeter constraints means . There are no triangles when because then must be less than , implying that , contrary to . When , similar to above, must be less than , so this leaves the only possibility . This gives 3 triangles within our perimeter constraint. When , can be or , which gives triangles . Note that is a right triangle, so we get rid of it and we get only 2 triangles. All in all, this gives us triangles.
Final answer
C