2. Suppose A takes X liters and B takes (2 10-x) liters.

According to the meaning of the problem in the equation

0.72 x+0.58(2 10-x)/2 10 = 0.62

If x=60, a is 60L and b is 150L.

3. It can be obtained from 120 liter of original 30% alcohol solution, and the original alcohol is 36L.

Add 23L of water, and the total liquid * * * is 143L, so now the alcohol concentration = alcohol-liquid x 100% is about 25. 1%.

4. Evaporating water: 50 kilograms of salt water with a salt content of 10 can be obtained. If the original salt has 5 grams, it will become salt water with a salt content of 20%.

Suppose that the evaporated water has x grams: 0.2x=5, and x=25 is obtained.

50-25 = 25g of water needs to be evaporated.

It's almost the same with water. Do the math yourself.

This question is the same as the second one. Learn to calculate it yourself.

Hand, hope to adopt ~