The Total Utility (TU) for a certain consumer is given by TU = 250Q – 50Q2 – Q3. Derive the Marginal utility function (Graphically or algebraically) and find the consumption level at which the Marginal Utility equal to zero. Also calculate the corresponding Total Utility?

Assuming the variables are QA and QB, you would find the sum of the partial derivatives with respect to each of the variables:

MU = 5(2)(QA) + 3(2)(QB) = 10QA + 6QB

MU = 5(2)(QA) + 3(2)(QB) = 10QA + 6QB