1) A number a is said to be perfect if the sum of all its divisors (excluding n itself) is equal to n. An example of perfect number is : A) 6 B) 9 C) 15 D) 21 Answer: Option AExplanation:Let the number be n Divisors of the number:6: 1, 2, 3 and its sum 1+2+3 = 69: 1, 3, 9 and its sum 1+3+9 = 1315: 1, 3, 5, 15 and its sum 1+3+5+15 = 2421: 1, 3, 7, 21 and its sum 1+3+7+21 = 32 So the n is 6
