Find the number of maps f: 1,2,3 1,2,3,4,5 such that f(i) f(j) whenever i < j

Step-by-step solution

array ll f(i) f(j) & i < j ( array l 1 2 3 array ) & ( array l 1 2 3 4 5 array ) array aligned & y₁+y₂+y₃+y₄+y₅=3 & ³⁺⁴ C₄= ^7 C₄=35 aligned