Combinatoricshard
0:00.0
Find the number of solutions to x₁ + x₂ + x₃ + x₄ = 15 where each xᵢ is a non-negative integer and x₁ < x₂ < x₃ < x₄.
Find the number of solutions to x₁ + x₂ + x₃ + x₄ = 15 where each xᵢ is a non-negative integer and x₁ < x₂ < x₃ < x₄.