Find the sum of the positive divisors of 18.
The positive divisors of 18 are the positive integers that divide 18 evenly, without leaving a remainder. One way to find them is to list the factors of 18 in pairs, starting from the smallest and largest ones. The first pair is 1 and 18, since 1 times 18 is 18. The second pair is 2 and 9, since 2 times 9 is 18. The third pair is 3 and 6, since 3 times 6 is 18. There are no more pairs, since 4, 5, 7, and 8 do not divide 18 evenly. So the positive divisors of 18 are 1, 2, 3, 6, 9, and 18. To find their sum, I just add them up: 1 + 2 + 3 + 6 + 9 + 18 = 39. 