The sixth grade of primary school. In the sixth grade of primary school, it was not a concentration problem, but a percentage application problem. It is one of the problems of percentage application. In the sixth grade mathematics, most of the problems are the percentage of sugar water and salt water. In addition, there is the problem of proportional distribution of pesticides, which is actually the application of concentration.

Concentration problem is a special kind of percentage application problem, which has its own unique quantitative relationship and solution method. Before solving the problem, it is necessary to master the relationship among solute, solvent and concentration. Moreover, dilution is a common problem in solution proportioning, and the basic relationship to be mastered when diluting is that the solute quality remains unchanged before and after dilution.

To solve the concentration problem, we use the method of solving percentage application problems, that is, find out the invariants, apply the formula directly to simple problems, and then apply the formula to calculate after transforming complex problems.

Examples of concentration problems

Grandpa has 50g 16% sugar water.

How many grams of water does it take to dilute (1) into 10% sugar water?

(2) How many grams of sugar do you need to add to make it 30% sugar water?

Solution: (1) How many grams of water do you need? 50× 16%÷ 10%-50=30 (g).

(2) How many grams of sugar do you need? 50×( 1- 16%)↓( 1-30%)-50 = 10(g)。

Answer: (1) It needs 30 grams of water. (2) Need to add 10g sugar.