Marginal propensity to consume can be calculated as :

The correct answer is Option (3) → \( \displaystyle\frac{\Delta C}{\Delta Y} \)

The marginal propensity to consume (MPC) is the change in consumption per unit change in income. So it is the change in consumption (ΔC) divided by the change in income (ΔY). If income rises by Rs. 100 and consumption rises by Rs. 80, the MPC is 0.8.

C/Y is the average propensity to consume, which is consumption per unit of income.