Marginal rate of Substitution (MRS):
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It is the rate of exchange between two goods which are equally preferred.
It indicates the absolute amount by which one good is decreased or replaced to add one unit of another good.
Alternatively, the quantity of one good to be sacrificed or given up in order to gain another good by one unit, in process of substitution.





Conclusion:
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At Combination C, MRS=PR is observed. So, this combination is the least cost combination. Therefore, the consumer should buy 3 kg of apple and 2 kg of chiku.