If n (A) = 20; n (B) = 8; n (A ∪ B) = 28, then n (A ∩ B) is

(2 + 3) + 5 = 2 + (3 + 5) obey the law of

Number of subsets of a set contains “n” elements is

If 3p = 5q, then what is p : q ?

If 21 cows eat equal to 15 oxen, how many cows will eat equal to 25 oxen?