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Schedule of Law of Diminishing Marginal Utility
| Units | Total Utility | Marginal Utility |
| 1st glass
2nd glass 3rd glass 4th glass 5th glass 6th glass |
20
32 40 42 42 39
|
20
12 8 2 0 -3
|
From the above table, it is clear that in a given span of time, the first glass of water to a thirsty man gives 20 units of utility. When he takes second glass of water, the marginal utility goes on down to 12 units; when he consumes fifth glass of water, the marginal utility drops down to zero and if the consumption of water is forced further from this point, the utility changes into disutility (-3).
Here it may be noted that the utility of then successive units consumed diminishes not because they are not of inferior in quality than that of others. We assume that all the units of a commodity consumed are exactly alike. The utility of the successive units falls simply because they happen to be consumed afterwards.