I've already asked departmental colleagues this question, but no one had an answer. When choosing a pivot, the AQA text book (Discrete Mathematics 2) says "Select any column (except the last one) whose top element is negative"......However a question which then follows only produces an optimal solution if a pivot is selected from the y column as shown below P x y s t l 1 -1 -4 0 0 0 0 1 <u>3</u> 1 0 15 0 2 1 0 1 12 This correctly produces x=0 and y=5 gives P=20, but taking a pivot from the x column doesn't lead to this answer. I have browsed the net and found that some sites suggest you must take a pivot from the column with the most negative value. However this is clearly not always necessary and even on-line simplex engines don't always do this. Any suggestions on what I can say to my students who have stumbled into this problem?