List all possibilities first:

Our four possibilities: X 1+X2, Y 1+Y2, X 1+Y2, X2+Y 1.

There are two possibilities for suppliers: X 1+X2 and y1+y2;

* * * There are eight combinations (considering that there are actually only six rules).

Self: Supplier:

1, X 1+X2 X 1+X2 condition: x1> Y 1，X2 & gt； Y2 Expense Variance: 0

2.X 1+X2 Y 1+Y2 condition: x1> Y 1，X2 & gt； Y2 X 1+X2 must be >: Y 1+Y2 does not exist.

3.Y 1+Y2 X 1+X2 condition: y1> X 1, Y2 & gtX2 Y 1+Y2 inevitably >: X 1+X2 this item does not exist.

4.Y 1+Y2 Y 1+Y2 condition: y1> X 1, Y2 & gtX2 Expense Variance: 0

5.X 1+Y2 X 1+X2 condition: X 1 >Y 1, Y2 & gtX2 cost difference: Y2-X2.

6.X 1+Y2 Y 1+Y2 condition: x1> Y 1, Y2 & gtX2 cost difference: X 1-Y 1.

7.X2+Y 1 X 1+X2 condition: y1> X 1，X2 & gt； Y2 cost variance: Y 1-X 1.

8.X2+Y 1 Y 1+Y2 condition: y1> X 1，X2 & gt； Y2 Expense Variance: X2-Y2

At this time, the concept of density = weight-volume density is positive:+density is negative:-total density = total weight-total volume introduction.

Profit and loss balance condition: the total density of the first batch of goods and the second batch of goods.

Case 1: 0++/

Case 4: 0-/

Case 5: Earn Y2-X2 ++

Scenario 6: Earn X 1-Y 1+-

Case 7: Earn Y 1-X 1-++

Case 8: Earn X2-Y2-+-

Conclusion:

1, the density is equal to the positive and negative (same number);

2. Profits with different densities:

3. When making a profit:

The total density is positive, earning a negative density value;

If the total density is negative, a positive density value is obtained;

4. When making a profit

It will always be the one with smaller difference in profit (weight and volume)!