In fact, you can understand it this way. Xiao Ming finally drank everything, including 65,438+0 cups of milk (assuming the volume is 65,438+0). The first time he drank 30%, he added 30% water. The second time he drank 25%, he added 25% water and * * * added 55% water, so the water he drank was 1 * 55.

This is a gradual understanding. Let the amount of raw milk be 1, after drinking 30% first, the remaining amount of milk be 1- 1*30%=0.7.

After adding water, milk is 0.7, and water is 1-0.7=0.3. After drinking 25%, milk 0.7*25%=0. 175, water 0.3*25%=0.075, milk 0.7-0. 175 = remaining in the cup.

The last water added is 1-0.525-0225=0.25.

It can be seen that Xiaoming drinks 1 milk, 0.075+0.225+0.25=0.55 water, and milk drinks more.

I wonder what grade you are in. I wonder if we should consider the gap between molecules and atoms in chemistry? If not, the one above will do. Just take it with you if necessary. I hope it helps you.