Slack

Dear Tutor, For critical constraints (zero slack), then gaining additional units of these scarce resources will allow the optimal solution to be improved (e.g. higher contribution earned). Similarly if another department wants these resources then it will result in lower contribution- why contibution is lowered if another department requires it? Shadow prices are only valid for a small range before the constraint becomes non-binding or different resources become critical--what does a small range before the constrain becomes non-binding mean here? the shadow price of a constraint that is not binding at the optimal solution is zero--This means that non-critical constraints will have zero shadow prices as slack exists already?