A practical problem in children's summer homework There are 45 students in a class. Each of them has taken part in one or two of the writing class and the painting class. It is known that there are 25 students in the writing class and 25 students in the painting class. How many of them have taken part in both?

9-2=7 63/7=9 2*9=18 9*9=81
The answer is 18 / 81

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