Suppose 70 of the families in a certain town have children 3

Suppose 70% of the families in a certain town have children, 30% of the families have children under 6 years old, and 60% have children who are 6 years or older. What percentage of families have children both over 6 and under 6?

Please help me with this problem. Show me how to solve it, thank you

Solution

Define A =  families who have children under 6 years old

Define B = families who have children who are 6 years or older

P(A and B) = P(A) + P(B) - P(A or B)= 0.3 + 0.6 - 0.7 =0.2

=> 20% of families have children both over 6 and under 6