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