Girls require Time and Money:

1. Girls = Time x Money

Time is Money:

2. Time = Money

Substitution property:

3. Girls = Money x Money = (Money)^2

Money is the Root of all Evil:

4. Money = sqrt(Evil)

Square 4 and substitution property:

(Money)^2 = sqrt(Evil)^2 = Girls

Therefore:

5. Girls = Evil

Math!