1, memorize and understand the concentration calculation formula:

Salt content = the weight of salt; The weight of salt water.

The weight of salt water = the weight of salt+the weight of water.

2. Distinguish the changed quantity from the unchanged quantity in the brine.

There are three quantities of salt, water and brine in brine, and finding a constant quantity is the key to solve the problem.

For example, when salt is added to salt water, the salt changes, so does the salt water, and the water remains the same.

When salt water is added, the water changes, the salt water changes accordingly, and the salt remains the same.

Salt water evaporates, water changes, salt water changes, and salt remains unchanged.

Example:

There are two bottles of salt water of the same weight. The ratio of salt to water in the first bottle is 1: 3, and that in the second bottle is 3:2. After mixing two bottles of salt water together, the ratio of salt to water is (). (Nanshan bilingual true volume)

A.4:5 B.5:4 C. 17:23 D.25:24

Analysis: The amount of salt and water in this problem is different, but the weight of two bottles of salt water is the same, so the weight of salt water is the key to solving the problem.

The first bottle of salt: water = 1: 3, salt 1, water 3 and brine 4.

The second bottle of salt: water = 3: 2, 3 parts of salt, 2 parts of water and 5 parts of salt water.

Because the weight of two bottles of brine is the same, the number of bottles of brine can be changed to the same by finding the least common multiple. The least common multiple of 4 and 5 is 20, so it can be changed to 20.

The first bottle of salt: water = 1: 3 = 5: 15, 5 parts of salt, 0/5 part of water/kloc-0, and 20 parts of brine.

The second bottle of salt: water = 3: 2 = 12: 8, salt 12, water 8 and brine 20.

After mixing, there are 5+ 12= 17 parts of salt, 15+8=23 parts of water and 20+20=40 parts of brine.

So salt: water = 17: 23.