Question 35
How many ordered quadruples $(a, b, c, d)$ of four distinct numbers chosen from the set $\{1,2,3, \ldots, 9\}$ satisfy $b\lt a$, $b\lt c$, and $d\lt c$?
MathNet 2009-part-05 — 172 problems (EN–VI) Question 35
Math Olympiad Vault · MathNet 2009-part-05 — 172 problems (EN–VI)