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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?

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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 at 6:31

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up vote 6 down vote accepted

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

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

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

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