Assertion (A) is correct because if the Marginal Propensity to Save (MPS) is 0.5, then the Marginal Propensity to Consume (MPC) will also be 0.5 (since MPC + MPS = 1). However, Reason (R) is incorrect as it suggests that the sum of MPC and MPS is always equal to unity, which is true only under certain conditions and not in all cases.