There are 21 people who do the first question correctly and 18 people who do the second question correctly. How many people do both questions correctly?

There are 21 people who do the first question correctly and 18 people who do the second question correctly. How many people do both questions correctly?

"Spring free man" Hello, very happy to answer for you!
The teacher gave two math problems. Among the 30 students, 21 got the first problem right and 18 got the second problem right. How many got both problems right?
21 + 18-30 = 9 (person)
A: nine people got both questions right
I hope my answer will help you~