Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

It's been a long time since I've done algebra. I remember how to do it, but I'm at a loss to explain it. For instance, my son has the following problem; $$\frac{3}{Q+1}+\frac{2}{Q}$$ So I say, you just have to find a common denominator (like when you add "regular" fractions). All you need to do is this; $$\color{red}{\frac{Q}{Q}}\frac{3}{Q+1}+\frac{2}{Q}\color{red}{\frac{Q+1}{Q+1}}$$ What is this called?

share|cite|improve this question
Important detail: a "problem" really needs an English-language direction or question of what to do, and you didn't include that. You cannot look at a mathematical expressions and infer "what to do" from it, so pay attention to the actual directions. A short example I run in class is to ask: "What's the degree of $3x^2 + 5x^2$?", and a lot of students answer, $8x^2$, which isn't a degree at all. – Daniel R. Collins Sep 21 '15 at 6:31
up vote 6 down vote accepted

You said it: it's called "finding a common denominator".

share|cite|improve this answer

"Finding the least common multiple of both these denominators" and multiply the denominators to get the least common multiple.

share|cite|improve this answer
Ah, so it is like adding two "regular" fractions where the denominators have no common factors. – uncle brad Oct 16 '12 at 23:04

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.