Every day, a farm invests 5 yuan's funds in feed, equipment and manpower. It is estimated that an 80kg pig can gain 2kg every day. At present, the market price of live pigs is 8 yuan per kilogram, but it is predicted that it will decrease by 0. 1 yuan per day. When should the farm sell such pigs to get the maximum profit? (15)

Solution: the profit of selling this kind of pig (pig with initial weight of 80 kg) on T day is Z yuan.

Input per pig: 5t yuan.

Output: (8-0. 1t)(80+2t) yuan.

Profit: z = 5t+(8-0.1t) (80+2t) =-0.2t2+13t+640.

=-0.2(t^2-65t+4225/4)+3405/4

When t=32 or t=33, Zmax=85 1.25 (yuan)

Therefore, if such pigs are sold after the 32nd day, they can get the biggest profit.