The answer "yes" applies to addition, subtraction, and multiplication. This is because we can take any two integers and add them to get some other integer
eg: 5+7 = 12
We can subtract two integers to get some integer
eg: 9-1 = 8
And we can multiply two integers to get an integer
eg: 4*6 = 24
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The only one that isn't closed is division. We can divide some integers to get another integer
eg: 10/2 = 5
but there are cases where dividing two integers does not lead to another integer
eg: 8/5 = 1.6
The result 1.6 is not an integer since it has a decimal part
Also, the example your teacher provides has
1/6 = 0.167 approximately which is also not an integer
