# Week 14 – Adding and subtracting rational expressions and equations

This week in pre-calc, we learned how to add and subtract ration equations and expressions in 4 easy steps.

1. Determine the lowest common denominator (LCD). The lowest common denominator is the number 2 denominators have in common when they’re multiplied. So if 3 and 4 were in the denominator, the lowest common denominator is 12. Its like lowest common multiple. The first number they have in common when multiplied.
2. Rewrite each equation with the LCD in the denominator. When you find the lowest common denominator, you multiple each fraction by the LCD until you get the same denominator for all the fractions. You also need to multiply the numerator as well so you can add or subtract all your numbers over one common denominator.
3. Solve. After rewriting the question, you can simply the whole equation by collecting all your like terms and adding or subtracting them together all under your LCD.
4. Reduce if possible. You can reduce your equation only if it can be reduced on the top and bottom by the same number.