Discrete Math : Number of Solutions to Equations - a) Let n and r be positive integers. Explain why the number of solutions of the equation x1 + x2 + … + xn = r, where xi is a nonnegative integer for i = 1, 2, 3, …, n, equals the number of r-combinat ...
Using Permutations and Combinations - How many distinct nonnegative integer solutions are there to the equation x1 + x2 + x3 =7 in which x1 is greater than or equal to 3.