The average of three numbers is 15. If two numbers are 7 and 28 the third is

3¾ of 1280 + .......... = 250% of 2000

7200 ÷ 18 × 0.2 is equal to

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