500 yuan invested in early August is not calculated according to the current rate of return, but according to the original 500 yuan, so the return on investment in early August is 500 *( 18%)=-90 yuan.

The second question:

After 19 made a profit in April, assuming that you have invested 10 month and * * invested 5,000 yuan, your income is 5,000 * (1+21%) = 6,050 yuan. However, it should be noted that the fees and other issues are not considered here, and the actual income may be there.

The third question:

If you continue to make a fixed investment after making a profit, your fixed investment amount will be invested according to the original amount, so if you continue to make a fixed investment, your income will increase on the basis of the original income. And if you make a profit when the rate of return drops to 10%, then your income is the amount you originally invested multiplied by the rate of return 10%, that is, 5000* 10%=500 yuan.

The fourth question:

The present value coefficient of early annuity is used to calculate the present value of early annuity, not to calculate the investment income. The present value coefficient of advance annuity is calculated according to the income per period, discount rate and the number of periods of advance annuity, which is used to represent the sum of the present value of income per period of advance annuity.

I hope the above answers can help you.