(2) The sales volume is 8+4× 0.5 x, z=y× sales volume, and the functional relationship is listed;

(3) According to the functional relationship in (2), the value of the maximum profit sum x at this time is obtained by using the properties of quadratic function;

Answer: (X means unknown X means multiplication)

(1) According to the meaning of the question, y = 29-x-25 =-x+4 (0 ≤ x ≤ 4);

(2) According to the meaning of the question, z = yx (8+4× 0.5x) = (-x+4) (8+4× 0.5x) =-8x? +24X+32；

(3)∵z=-8X？ +24X？ +32=-8(X- 1.5)？ +50;

When x= 1.5 million yuan, the average weekly sales profit is the largest, at this time, 29-X=27.5,

That is, when the price of each car is 275,000 yuan, the average weekly sales profit is the largest, and the highest profit is 500,000 yuan;