# how to add/subtract than multiply fractions?

Q). 1 + 9/2 x -5/7

Q). 1 - y^2 x 9/4

just guide me how to solve this question

Edit: From the title of the question I would infer that he/she meant

$1 + \frac92 \times \frac{-5}{7}$

$1 - y ^2 \times \frac94$

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Your question is not clear because of how you've written it. Is the "x" a times symbol ($\times$) or a variable? Which things are intended to be in the denominator? Do you mean: $$1 + \dfrac{9}{2} \times \dfrac{-5}{7}\qquad \text{and}\qquad 1 - y^2 \times \dfrac{9}{4}$$ or $$1+\frac{9}{2} x-\frac{5}{7}\qquad \text{and}\qquad 1-y^2x\frac{9}{4}$$ or $$1+\frac{9}{2x}-\frac{5}{7}\qquad\text{and}\qquad 1-y^{2\times \frac{9}{4}}$$ or something else? –  Zev Chonoles Feb 1 '13 at 12:43
You can find some good starting points on how to format mathematics on the site here and here. This AMS reference is very useful. If you need to format more advanced things, there are many excellent references on LaTeX on the internet, including StackExchange's own TeX.SE site. –  Zev Chonoles Feb 1 '13 at 12:48

You need to put some brackets to "change" the precidence.

.i.e.

$(1+\frac{9}{2}) \times \frac{−5}{7}$

$(1 − y^2) \times \frac94$

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Thanks for the help. :) –  Franco Feb 1 '13 at 14:13

to add or subtract fractions they need to have a common denominator. For your first question for instance multiply $\frac{9x}{2}$ by 7 on the top and bottom to get $\frac{9x}{2}=\frac{63 x}{14}$, then multiply $\frac{5}{7}$ by 2 on the top and bottom to get $\frac{5}{7}=\frac{10}{14}$. Now you have two fractions with a common denominator and you can just add/substract the numerators. Similarly you can use $1=\frac{1}{1}=\frac{14}{14}$. In general to do $\frac{a}{b}+\frac{c}{d}$ you change it to $$\frac{a}{b}+\frac{c}{d}=\frac{ad}{bd}+\frac{cb}{db}=\frac{ad+cb}{bd}$$ To multiply fractions you simply multiply the numerators and denominators with each other: $$\frac{a}{b} \cdot \frac{c}{d}=\frac{ac}{bd}$$ Just like with normal numbers you usually first multiply/divide then add/substract, except when there's brackets of course in which case you need to work these out first. Hope this helps! I dont want to spell out the answers for you because I think you can do it!

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+1 $~~~~~~~~~~~~~$ –  Babak S. Feb 1 '13 at 12:47
Thanks for the help. :) –  Franco Feb 1 '13 at 14:14
No problem, glad to help! These things become second nature after a while :) –  Slugger Feb 1 '13 at 18:20