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Algebra

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Hi, I'm looking at my book and I can't see how they've gotten this answer:

The last bit:

-11/20y=-3

Their answer is y=60/11

How did they get that?

The full problem, if it helps:
1/4y+2=4/5y-1
1/4y-4/5y=-1-2
-11/20y=-3
y=60/11

Okay, since typing it out - I see that they've multiplied the 20 times the -3. But why? I'm worried I won't know when do to it this way.

  • Algebra -

    Did you check my answer to you this morning? I went to bed before I saw your last question. You have to keep the equal sign and zero even if you have zero on the right.
    Anyway
    -11/20 y = -3
    multiply both sides by 20
    -11 y = -60
    divide both sides by -11
    -11/-11 y = -60/-11
    y = 60/11

  • Algebra -

    Now about yesterday :

    #


    They're saying 2 is right. I'm so confused.

    # Algebra - Damon, Sunday, January 25, 2009 at 6:34am

    MINE:
    3y-18=-6y
    3y+6y-18=-6y+6y
    9y-18 BUT continue with right 9 y - 18 = 0
    9y/9 = -18/9 BUT then add 18 both sides 9 y=18
    y=-2 BUT I GET then y = 2

  • Algebra -

    You multiply both sides by 20 to get rid of the 20 under the y.
    You want to get y alone on the left
    to get it alone, you need to multiply both sides by 20
    then divide by -11

    You could have done it all at once. multiply by -20/11

  • Algebra -

    It is getting late. I will check in the morning and see if you are catching on to this stuff. Others here may be able to help you in the meantime.

  • Algebra -

    Thanks. I understand the -11/20 problem and I'm redoing the one from last night. Something finally clicked in my brain, and I was able to finish my lab.

    Thank you for helping. <3

  • Algebra -

    Ok, good luck !

  • Algebra -

    Okay, I did it how you said 9y-18=0 then+18+18 and then 9y/9 = 18/9 y=2.

    So, it came out right. The only question I have is should I be adding a zero everytime? Where does it really come from?

    Sorry if it's a weird question. I'm pretty dyslexic with numbers and algebra just aggravates it. So, to be sure I can do it, I have to question every move I make. :\ But thank you for helping. :)

  • Algebra -

    3y+6y-18=-6y+6y
    Right here you added 6 y to both sides to make the right hand side of the equation zero.
    You still have the equal sign and the zero that results from -6y+6y
    so on the right you have to include that =0

    The whole thing with algebra is you work with both sides of the equal sign to get what you want to find all by itself on one side.
    You may not eliminate the equal sign itself or whatever is on one side of it. If it happens to be zero on one side, write = 0

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