Question

A survey of a group of children, revealed that 80 of them liked at least one of the cereals, Corn Flakes or Almond Flakes. If 50 of them liked Corn Flakes and 40 of them liked Almond Flakes How many liked both the cereals? 40 30 90 10

Answer 1

$n(A \cup B) = n(A) + n(B) - n(A \cap B)$

Putting the values,

$80 = 50 + 40 - n(A \cap B)$

So, $n(A \cap B) = 10$

So 10 people liked both cereals.

** If the answer does not match please comment.