The human wealth and total wealth of Doraemon and Nobita over the next three years are calculated as follows:
For Doraemon:
Human Wealth (HW) = Present Value of Future Salary
HW = \frac{Salary_{1}}{(1+r)} + \frac{Salary_{2}}{(1+r)^2} + \frac{Salary_{3}}{(1+r)^3}
Where Salary_{1}, Salary_{2}, and Salary_{3} are the salaries for the next three years after tax and adjusted for real growth, and r is the real interest rate.
Salary after tax = Annual Salary * (1 - Tax Rate)
Real Salary Growth = Salary after tax * (1 + Real Growth Rate)
For Year 1:
Salary_{1} = 700,000 * (1 - 0.20) * (1 + 0.02) = 560,000 * 1.02 = 571,200
For Year 2:
Salary_{2} = 571,200 * (1 + 0.02) = 582,624
For Year 3:
Salary_{3} = 582,624 * (1 + 0.02) = 594,276.48
HW_{Doraemon} = \frac{571,200}{(1+0.20)} + \frac{582,624}{(1+0.20)^2} + \frac{594,276.48}{(1+0.20)^3}
HW_{Doraemon} = \frac{571,200}{1.20} + \frac{582,624}{1.44} + \frac{594,276.48}{1.728}
HW_{Doraemon} = 476,000 + 404,600 + 343,800 \approx 1,224,400
Total Wealth (TW) = Human Wealth + Nonhuman Wealth
Since Doraemon has no nonhuman wealth, TW_{Doraemon} = HW_{Doraemon} = 1,224,400
For Nobita:
Nobita's human wealth is calculated similarly to Doraemon's, but Nobita also has nonhuman wealth from the bonds.
Nonhuman Wealth (NHW) = Present Value of Bonds
NHW_{Nobita} = \frac{500,000}{(1+r)} = \frac{500,000}{1.20} = 416,666.67
HW_{Nobita} and TW_{Nobita} are calculated similarly to Doraemon's, with the appropriate salary.
TW_{Nobita} = HW_{Nobita} + NHW_{Nobita}
(b) An increase in the tax rate to 40% would reduce the after-tax salary for both Doraemon and Nobita, thus reducing their human wealth. Since Nobita has nonhuman wealth, the impact on his total wealth would be less severe compared to Doraemon, who relies solely on human wealth. Their permanent consumption levels would decrease as their disposable income decreases due to higher taxes.
Human wealth is the present value of future income streams, while total wealth includes both human and nonhuman wealth. The present value is calculated by discounting future values at the real interest rate, and adjustments are made for taxes and real salary growth. An increase in the tax rate reduces disposable income, affecting both human wealth and permanent consumption levels.