This is a difficult problem in the application of economic mathematics, and the key point is to grasp the relationship among equivalence, function and equation.

(1) Obviously, W is a function of X, and 12 tons of strawberries were purchased, X tons were packed in Class A and (12-x) tons were packed in Class B..

Cost part:

Acquisition cost = 12X 1= 12 (unit: ten thousand yuan, the same below).

X tons of Class A packaging, packaging cost = X.

For (12-x) tons of Class B packaging, the deep processing cost is s=2( 12-x)+6=-2x+30.

Income part

The price of grade B strawberries =5( 12-x)=60-5x.

Strawberry price:

When 2 ≤ x

When x≥6, the selling price = 2.5x.

therefore

w=-x？ +8x+(60-5x)- 12-x-(-2x+30)

w=-x？ +4x+ 18(2≤x & lt； 6)

w = 2.5x+(60-5x)- 12-x-(-2x+30)

w =- 1.5x+ 18(6≤x≤ 12)

When 2 ≤ x

Maximum value w = 22> 14.

Suppose x = 6, and the quadratic function value of w: w = 6.

W is 2 ≤ x

(2) according to the meaning of the question

Of the 300,000 yuan, A is used for Class A packaging.

Then the number of strawberries packaged in class A * * * =a/2.

There is also (30-a) for Class B packaging [difficult! ]

There are t tons of strawberries in Class B package.

(30-a)/(2t+6+ 1)=t

30-a=2t？ +7t

a=-2t？ -7t+30

A is a quadratic function about t, so this problem can only be expressed as a function of actual income W.

So, the tonnage of grade A strawberries is b=-t? -7t/2 + 15

The vertex of this function is at point T.

Maximum t=0, b= 15.

As investment capital, a≥0, when a=0, -2t? The solution of -7t+30=0 is t 1

When b=6, t 1

So the sales revenue of grade A strawberries =-b+8=-t? -7t/2+23(0≤t & lt； 1)

Or =2.5b=2.5(-t？ -7t/2 + 15)=-5t？ /2 - 35t/4 + 75/2 ( 1≤t≤6)

The price of grade B strawberry is 5t.

finally

At this time, the sales expenses-300,000 yuan, profit.

w 1=-t？ -7t/2+23+5t-30(0≤t & lt； 1)

=-t？ +3t/2-7(0≤t & lt； 1)

The opening is downward, and the maximum value is t=3/4.

At this time, the income =- 103/ 16.

w2=-5t？ /2-35t/4+75/2+5t-30( 1≤t≤6)

=-5t？ /2 - 15t/4 + 15/2

Open down, fix the point T.

The maximum value is t= 1, and w2=5/4.

To sum up, we need to buy 1 ton of B-grade processed strawberries, and1-7/2+15 =10.5 ton of A-grade strawberries.

At this time, the income is 5/4= 1.25 million yuan.