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Need a Refresher on Algebraic Sign Operations

Problem Solving — algebra and arithmetic (GMAT Focus Edition)
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Need a Refresher on Algebraic Sign Operations

by BlindVision » Tue Mar 10, 2009 3:27 pm
It's been aeons since I've taken Algebra and wanted to kindly ask for help on refreshing the alegabraic sign operations...

1) -1(-8) = +8 ?

2) -(-8) = +8 ?

3) Can -y +8 be rewritten to y - 8 ?

4) Can -y - 8 be rewritten to y + 8 ?

I know it sounds silly of me to ask these questions but I really don't want to get any fundamental operations wrong on the real thing! Thank you for not laughing :D
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Re: Need a Refresher on Algebraic Sign Operations

by Ian Stewart » Tue Mar 10, 2009 4:26 pm
BlindVision wrote:It's been aeons since I've taken Algebra and wanted to kindly ask for help on refreshing the alegabraic sign operations...

1) -1(-8) = +8 ?

2) -(-8) = +8 ?

3) Can -y +8 be rewritten to y - 8 ?

4) Can -y - 8 be rewritten to y + 8 ?

I know it sounds silly of me to ask these questions but I really don't want to get any fundamental operations wrong on the real thing! Thank you for not laughing :D
A great way to learn is to ask - no one will laugh here!

Both 1) and 2) above are perfectly correct. When you multiply two negatives together, you will always get a positive.

In 3) and 4), however, when you reverse every sign, you are actually finding the negative of the expression you start with - you've multiplied each expression by -1. You can see this easily enough by choosing a number for y. Look at 3), and plug in y = 4. Then -y + 8 = -4 + 8 = 4. On the other hand, y - 8 = 4 - 8 = -4. The same will happen with the expression in 4) if you plug in any number you like for y.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

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by cramya » Tue Mar 10, 2009 5:02 pm
BlindVision,
Nothing wrong with getting the basics confirmed and what better place could we chooose than a wonderful forum like this.

You may find the website below useful too (for GMAT QUANT):

https://www.purplemath.com/modules/index.htm

Regards,
CR
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by BlindVision » Tue Mar 10, 2009 9:18 pm
Ian & Cramya! You guys are the best! Man... you guys sure make me feel at home. If I ever write a success story [which I'm determined to do so], you better believe both of your names will be in it!!!!!:D
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