2. This calculation doesn't make any sense. It is impossible for a fund with pure debt to maintain a constant income of 5%, and there may be losses. Monetary funds are still stable, but they are not static.

3. I still want to tell you the calculation method:

Except for the first month and every other month after that, 800 yuan can be calculated on a monthly basis, and the monthly interest rate is (5/ 12)%, so let's calculate it on a monthly basis.

First month: 800 * {1+(5/12)%} (18 *12)

Second month: 800 * {1+(5/12)%} (18 *12-1)

Third month: 800 * {1+(5/12)%} (18 *12-2)

. . . .

Last month: 800

Then add it up. . . In fact, there is a summation formula, which I forgot. There is no need to look for it.