2. Fill a 30 ml cup and pour a 70 ml cup.
3. Fill the 30 ml cup and fill the 70 ml cup.
4. Pour all the water in the 70 ml cup into the original cup, and pour all the water in the 30 ml cup into the 70 ml cup. At this time, the original cup has 80 ml, the 30 ml cup is empty and the 70 ml cup has 20 ml. Fill the 30 ml cup. At this time, the original cup contains 50 ml, the 30 ml cup is full and the 70 ml cup contains 20 ml.
5. Pour all the water in the 30ml cup into the 70ml cup. At this time, the original cup contains 50 ml, the 30 ml cup is empty, and the 70 ml cup contains 50 ml.
This problem uses addition and subtraction in mathematics.
Think about solving problems:
This problem is actually very simple, mainly using addition and subtraction in mathematics.
Extended data:
Multiplication is a simple operation of addition and division is a simple operation of subtraction.
Subtraction and addition are reciprocal operations, and division and multiplication are reciprocal operations.
Integer addition and subtraction algorithm;
(1) Same-digit alignment;
(2) from the unit;
(3) When it is added to dozens, it will be pushed to a higher position; If the subtraction is not enough, subtract 1 from the high position. When this number is added to 10, it will decrease.
Properties of addition operation
From additive commutative law's associative law, it can be concluded that when several addends are added, the positions of addends can be exchanged at will; Or add a few addends first and then add them with other addends, and the sum remains the same. For example: 34+72+66+28 = (34+66)+(72+28) = 200.