There are 30 students enrolled in a math class and each of them attended at least one of the first two lessons. The first lesson was attended by 27 students and the second lesson was attended by 20. How many students attended both of the first two lessons?

Question

anonymous · Answer

I'm pretty sure the answer is 13, however, I need to show it using discrete math.

inkyvoyd · Answer

set theory ayay

anonymous · Answer

yeah, but I'm not sure how to go about it.

inkyvoyd · Answer

@phi  u knows math rite

phi · Answer

I think you should draw a Venn diagram

one circle is class 1  and the other is class 2

phi · Answer

|dw:1378164962638:dw|

anonymous · Answer

Wow, makes sense now, thank you! :)