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SMO 2014 Open Round 1 Question 12

SMO · SMO 2014 Open Round 1

Question 12

Find the number of triples $(a,b,c)$ such that $a,b,c$ are numbers in the set $\{1,2,3,\ldots,15\}$ satisfying the conditions $a\lt b-1$ and $b\lt c-2$.