First, fill a nine-liter bucket with water, then fill a four-liter bucket with nine liters of water, so that there are five liters of water left in the nine-liter bucket, then pour out the water in the four-liter bucket and fill the remaining water in the nine-liter bucket with four liters of water. At this time, you can get that there is a liter of water in the nine-liter bucket.

Then pour out the water from the four-liter bucket, pour one liter of water from the nine-liter bucket into the four-liter bucket, fill the nine-liter bucket with water, and finally fill the four-liter bucket with water. Because there is one liter of water in a four-liter bucket, three liters of water are poured out in a nine-liter bucket, and six liters of water are left in the bucket.

Extended data

Mathematical thinking teaching is a dynamic mathematical learning activity. Mathematics teachers guide students to carry out specific mathematical thinking and mathematical operations according to mathematical materials, and form mathematical perception, which is what we often call "number sense".

For example, there are eight birds and four fly in. This is the math material. According to these materials, mathematical concept is mathematical thinking. For example, there used to be eight birds, four more flew and a few less flew. There used to be eight birds, and four more flew in, a few fewer than before, and four more flew in, several times more than before.

Baidu encyclopedia-mathematical thinking