Question

In a class of 40students,23 offer biology and 27 offer chemistry.Each student offers at least one of the two subjects.How many students offer both subjects?

Answer 1

I think you're using the word "offer" incorrectly. The question should read as follows:
<i>In a class of 40students, 23 take biology and 27 take chemistry. Each student takes at least one of the two subjects. How many students take both subjects?</i>

Now please wait for a math tutor to help you with the problem itself.

Answer 2

If you just add up 23 and 27, then you have counted twice those who take both. So, if there are x of those, then
23+27-x = 40

Answer 3

40