Questions regarding Marginal Rate of Technological Substitution

To answer your first question it is helpful to rewrite the MRS as a ratio of the partial derivatives. What you are looking at is the slope of the Isoquant. If you plug in "real changes" of Q and L you will move along a linear approximation of the (usual) convex curve. begin{equation} MRS=frac{frac{delta Q}{delta L}}{frac{delta Q}{delta K}} approx frac{Delta Q}{Delta L} end{equation} Regarding your second question it is some kind of definition problem. I assume MRS KL means MRS from K to L. Or in other words how much capital is needed to compensate the loss of labor. If you change the denominator and nominator of the fraction you would than need to change the notation to MRS L to K instead of K to L.