(Answered) The consumers marginal rate of substitutuin is fThe consumers marginal rate of substitutuin is f

➤ Why does the MRS usually diminish as consumption of one good rises?
The MRS typically falls because of diminishing marginal utility. As you consume more X, each extra X gives less additional satisfaction relative to Y. Indifference curves are convex, reflecting a preference for balanced bundles. Convexity and decreasing marginal utility together produce a declining trade-off rate between goods.