Using the isoquant schedule, factor combination B uses 2 units of X with 8 units of Y, and combination C uses 3 units of X with 5 units of Y. The marginal rate of technical substitution (MRTS) of X for Y between B and C is:

1. MRTS of X for Y is the units of Y given up per extra unit of X added, holding output constant. 2. Moving from B to C, X rises by $3 - 2 = 1$ unit and Y falls from 8 to 5, a drop of 3 units. 3. So MRTS $= \frac{\Delta Y}{\Delta X} = \frac{3}{1} = 3$. 4. The value 4 is the MRTS for the A-to-B move and 2 is for the C-to-D move, so the answer here is 3. _Source: ICAI BoS CA Foundation Paper 4 Business Economics, Ch 3 Unit I "Theory of Production", p.22_