The corner points of the feasible region determined by the system of linear constraints are (0, 10), (5, 5), (15, 15), (0, 20). Let z = px + qy. Condition on p and q so that the maximum of z occurs at both the points (15, 15) and (0, 20) is
The number of functions f from {1, 2, 3, …, 20} onto {1, 2, 3, …, 20} such that f(k) is a multiple of 3 whenever k is a multiple of 4, is