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Help with simple equation question

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by [email protected] » Mon Nov 25, 2013 8:40 am
Hey,

Can you paste the complete question with the answer because two negatives divided should not give a negative solution for example -x/-y will always be x/y and not -x/y!!
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by Brent@GMATPrepNow » Mon Nov 25, 2013 8:45 am
jjohnson50 wrote:As I come to the end of an equation, I get:

-15=-6

From this point, what calculation doI use to get the final answer, which is:

-2/5

Thank you
I think you need a variable somewhere here, since -15 cannot equal -6


Let's say the equation is -15x = -6
We can isolate x by dividing both sides by -15 to get: -15x/(-15) = (-6)/(-15)
Simplify to get: x = 2/5

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by jjohnson50 » Mon Nov 25, 2013 8:55 am
Yes, you are right, sorry about that:

-15y=-6


y=-2/5

Thank you
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by Brent@GMATPrepNow » Mon Nov 25, 2013 9:27 am
jjohnson50 wrote:Yes, you are right, sorry about that:

-15y = -6


y=-2/5

Thank you
If the equation is -15y = -6, then y = 2/5 (not -2/5)

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by jjohnson50 » Mon Nov 25, 2013 9:44 am
Brent

Thanks for sticking with me on this:

-15y=-6

From this point, what calculation doI use to get the final answer, which is:

y=2/5

Thank you
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by Abhishek009 » Mon Nov 25, 2013 9:51 am
jjohnson50 wrote:Brent

Thanks for sticking with me on this:

-15y=-6

From this point, what calculation doI use to get the final answer, which is:

y=2/5

Thank you
Consider it this way -

-15y=-6

or, (-3)(5)y = (-3)(2)

Or, 5y = 2

Or, y = 2/5
Abhishek
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by [email protected] » Mon Nov 25, 2013 2:53 pm
Hi jjohnson50,

There's a rule in algebra that essentially says "if you do something to one side of an equation, you have to do it to the other side."

Here, we have -15y = -6

If we want to isolate the y, then we have to divide BOTH sides by - 15

So, we'd have -15y/-15 = -6/-15

On the left side, the -15s cancel out:

y = -6/-15

On the right side, the negatives cancel out and the fraction reduces (divide the numerator and denominator by 3)

y = 6/15 = 2/5

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by jjohnson50 » Mon Nov 25, 2013 6:55 pm
This explanation helped. Thanks!
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by Mathsbuddy » Tue Nov 26, 2013 1:59 am
Alternatively change the sign on both sides, then divide by 3, then divide by 5.
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