The sum of two numbers is 30. The first number is 1/2 the second number

Well ... its very simple, you can do it algebraically. If the first number is X and the second number is half of X then you have:

X + X/2 = 30

2X/2 + X/2 = 30 (2X/2 = X)

3X/2 = 30

3X = 60

X = 20

So the first number is 20, the second number is 10