There are 20 students in the mathematics group doing two mathematical thinking problems together. There are 10 students doing the first problem right and 15 students doing the second problem right. There are 2 students doing both problems wrong. How many students are doing both problems right?
20-2 = 18 (person)
10 + 15 = 25 (person)
25-18 = 7 (person)
Answer: there are 7 people who do both questions right
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