For any two sets A and B, what does A − (A − B) equal?

A and B are two sets. A has 10 members and B has 18 members. A ∪ B = 20. The number of members in A ∩ B will be

If p is the difference between a number and its reciprocal and q is the difference between the square of the same number and the square of its reciprocal, then what is p⁴ + 4p² equal to ?

What are the two natural numbers whose product is 2400 and the sum of whose squares is 5200?

Seven times a two-digit positive number is equal to four times the number obtained by reversing the order of the digits. How many such two-digit numbers are there?

The sum of the digits of a two-digit number is 9. If the digits of the number are reversed, the new number formed is 45 more than the original number. What is the original number?