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Mathematics 7300
At present, the total income from day 0 to day n is 7300 yuan.

Assuming that T day turns (7300t yuan), the investment income will be generated on the (t+4) day, and the income on the N day will be

f(t) = (n-(t+4)) * 7300t * 0.0005

F(t) is a quadratic form of T, and the parabola has a downward opening and a maximum value, which is obtained when t = n-(t+4), that is, t= (n-4)/2.

The constraint condition is to ensure that the income handling fee is positive, that is, F (t)-220 >; 0,

So f ((n-4)/2)-220 = ((n-4)/2) 2 * 3.65-220 > 0.

Get n > 19.5

So n = 20

t = (20-4)/2 = 8

Turn it every 8 days, so that by the next turn, you can ensure that the previous investment has produced positive returns.