Question

In a group of 80 people 50 do not drink coffee and 30 do not drink tea what can be the maximum number of people who drink both tea and coffee

Answer 1

total = 80
Do not drink Coffee = 50.   =>   Drink coffee = 80-50 = 30
Do not drink Tea = 30         =>  Drink  Tea  = 80 - 30 = 50

So maximum number of people who drink both Tea and Coffee = 30,
       as in sets:    A ∧ B  ⊆ A      and     A ∧ B ⊆ B