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Simple Inequalities Question

Problem Solving — algebra and arithmetic (GMAT Focus Edition)
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Simple Inequalities Question

by bdevas01 » Sat Jan 30, 2010 8:24 am
I was on platinumgmat.com, looking over their quantitative tutorials and I believe I have found an error, but I'd just like confirm it with the community.

The tutorial states the following:

"If x+2 < y+2 is multiplied by -1 on both sides, the result is not -2-x < -y-2. Instead, the result is -2-x > -y-2. "

I don't understand why the 'x' and the '2' on the left-hand side of the inequality have changed order. I believe it's a typo, but maybe I'm missing something.

What do you guys think?
The direct link to the site is: https://www.platinumgmat.com/gmat_study_ ... equalities

Thanks in advance for all posts!
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by thephoenix » Sat Jan 30, 2010 10:31 am
bdevas01 wrote:I was on platinumgmat.com, looking over their quantitative tutorials and I believe I have found an error, but I'd just like confirm it with the community.

The tutorial states the following:

"If x+2 < y+2 is multiplied by -1 on both sides, the result is not -2-x < -y-2. Instead, the result is -2-x > -y-2. "

I don't understand why the 'x' and the '2' on the left-hand side of the inequality have changed order. I believe it's a typo, but maybe I'm missing something.

What do you guys think?
The direct link to the site is: https://www.platinumgmat.com/gmat_study_ ... equalities

Thanks in advance for all posts!
hello devas

the operation is correct
in inequalities whenever u multiply or divide bth side by -1 the sign reverses.....

to understand this just consider x and y are int such that x<y ; now multiply bth side by -1 result will be -x>-y
for eg
x=2 and y=10
2<10
but -2>-10
hence multiplying -1 will rsult in change of sign
same is true with div....

moreover when x>y
we can not say x/Y>1
bcoz for -x and -y result will be opp...

but we can say x-y>0
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by bdevas01 » Sat Jan 30, 2010 11:09 am
Thank you for your reply but that was not my question. I understand that the sign changes but why do the x and the 2 switch places?
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by sars72 » Sat Jan 30, 2010 11:28 am
bdevas01 wrote:Thank you for your reply but that was not my question. I understand that the sign changes but why do the x and the 2 switch places?
it doesn't matter in which order they are. As long as they are on the same side.

-x-2 is the same as -2-x
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by bdevas01 » Sun Jan 31, 2010 8:06 am
That's true, I didn't catch that but now that you point it out, it makes sense. Subtracting a number from a negative number is the same thing as adding a number to a positive number (with the exception that one will yield a negative number and the other a positive number).

I'm just curious to know why the two numbers were flipped in the first place. Any ideas?
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by harsh.champ » Mon Feb 01, 2010 1:45 am
well,the catch in such questions is that you just have to put some values of x and y...suppose x is 2 and y is 3 ....then x+2 (4)<y+2(5).......but on the negative number line -4>-5...thus this is an objective way of getting to the answer.....and a pretty simple way too as it takes just 3-5 seconds to figure out
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by harsh.champ » Mon Feb 01, 2010 1:55 am
bdevas01 wrote:That's true, I didn't catch that but now that you point it out, it makes sense. Subtracting a number from a negative number is the same thing as adding a number to a positive number (with the exception that one will yield a negative number and the other a positive number).

I'm just curious to know why the two numbers were flipped in the first place. Any ideas?

well,flipping the numbers is just a way of confusing you and decreasing your speed......just keep your concepts clear
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by bdevas01 » Mon Feb 01, 2010 7:26 am
Got it.

Thanks for clearing it all up guys!
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