1, principle: before mixing, whole, amount x, indicating dose a whole, amount y, indicating dose b (a >; B) the mixed whole, quantity (x+y) and index quantity c can be obtained as follows: x×a+y×b=(x+y)c Deduction: x×(a-c)=y×(c-b) Get the formula: (a-c): (c-b) = y. When x+y is known, this method can also be used if x or y is known; It is ok to know x: y.

2. The essence of crossover method is a simple form of solving binary linear equations. This kind of problem can also be solved by equations. The specific method of using this rule is as follows: For example, the density of A is 10, the density of B is 8, and the density of their mixture is 9. You can put 9 in the middle, write 10 and 8 on the left, mark AB, and then subtract 9 respectively, and the right is 60. At this time, the ratio is 1: 1.