Answer:
Total Utility is total satisfaction from all units of consumption of a good. TU= ΣMU
Marginal Utility is additional satisfaction from additional unit of consumption of a good. Â MU = TUn - TUn-1
Average Utility is average satisfaction per unit of output consumed of a good. AU = TU/N
1. TU Increases at increasing rate : MU Â Increases Â
TU increases at decreasing rate : MU decreases
TU is maximum : MU is zero
TU is falling : MU is negative
MU > AU : AU increase
MU < AU : AU decrease
2. Consumer Optimum is where consumer gets maximum satisfaction from consumption of certain units of a good, any deviation from that yields lesser satisfaction from the optimum point.
3. Consumer Optimum is where : Marginal Utility of the good = Price of the good.
4. Q Â Â Â 0 Â Â 1 Â Â Â 2 Â Â Â Â 3 Â Â Â 4 Â Â Â 5
 TU    0  60   130  190  230  250
MU at 4th unit  = TUn - TUn-1 = TU4 - TU3 = 230 - 90 = 40
AU at 3rd unit  = TU / N = 190/ 3 = 63.3
AU at 5th unit = Â TU / N = 250/5 = 50