(2) The previous two years: 0≤x≤50. At this time, because P increases with the increase of X, when x=50, the maximum value of P is 400,000 yuan, so the maximum profit in these two years is 40× 2 = 800,000 yuan.

Last three years: if the annual profit is Y and the local investment is X, the foreign investment is 100-X, so Y = P+Q.

=+= =, which means that when x=30, Y is the largest, which is 1065, so the maximum profit in three years is1065× 3 = 34.95 million yuan.

So the maximum profit in five years is 80+3495-50× 2 = 34.75 million yuan.

(3) It has great practical value. [Come]