Total Utility at any unit is simply the running (cumulative) sum of Marginal Utility up to that unit. …

Since Total Utility is the sum of all Marginal Utilities consumed so far ($TU_n = MU_1 + MU_2 + \dots + MU_n$), TU at each unit is obtained by cumulatively adding the MU figures:

• $TU_1 = MU_1 = 15$
• $TU_2 = TU_1 + MU_2 = 15 + 12 = 27$
• $TU_3 = TU_2 + MU_3 = 27 + 9 = 36$
• $TU_4 = TU_3 + MU_4 = 36 + 6 = 42$

Independent check (working backward): subtracting each TU from the next should recover the original MU figures — $27 - 15 = 12$; $36 - 27 = 9$; $42 - 36 = 6$ — each matches the given MU column exactly, confirming the cumulative addition was done correctly.

Alternative check: since MU is falling continuously in this data, TU must rise at a continuously diminishing rate — verified above, since each successive i …

Students sometimes treat MU and TU as unrelated columns and simply copy the MU figures as TU, forgetting that TU must be …