Which of the following numbers is a perfect number?

(a) 16
(b) 8
(c) 24
(d) 28

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Solution

(d) 28
A number for which the sum of all its factors is equal to twice the number is called a perfect number.
Factors of 28 are 1, 2 , 4, 7, 14, and 28.

Sum of factors of 28 = 1 + 2 + 4 + 7 + 14 + 28 = 56 = 2 × 28
Hence, 28 is a perfect number.

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