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Student 1: The operation of combining two numbers into one number is called addition.
Student 2: Knowing two numbers and one of the addends, the operation of finding the other addend is called subtraction.
2. Show: Mom cut a rope into two pieces, one is 83 cm long and the other is 59 cm long.
Teacher: Can you ask a math question and answer it according to the information provided by your mother?
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Student 1: How long is this rope? 83+59 = 142 (cm).
Student 2: What is the distance between two ropes? 83-59 = 24 (cm).
3. Teacher: These two topics are both integer addition and subtraction. Can you tell me what I need to pay attention to when calculating integer addition and subtraction?
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Student 1: aligned with single digits, starting with single digits. If the numbers on the digits add up to ten, the number on the previous digit will be entered as one.
Student 2: Same digit alignment, starting with single digits. If the number of digits is not reduced enough, it will be reduced from the last digit, combined with the standard figures, and then reduced.
4. Teacher: The students all recited the calculation method of integer addition and subtraction. If you change it to decimal addition and subtraction, can you still work it out? In this lesson today, we are going to learn the general calculation of decimal addition and subtraction. (blackboard writing: topic)