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Math Help - Need help with a word problem.

  1. #1
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    Mar 2009
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    Need help with a word problem.

    Problem: The Difference between 2 numbers is 15. If twice the larger number is added to 3 times the smaller, the result is 90. Find the 2 numbers.

    If I understood it correctly this would cause the formulas to be...
    x - y = 15
    2x + 3y = 90.

    I need to find the answer for x and y by using BOTH the addition method and substitution method. I keep thinking I have it until I go back and check my answer, then I keep finding out I'm completely wrong. I assume this problem is actually quite easy, but it's frustrating me. Any help would be appreciated.

    I need to show my work also. I really want to understand the steps involved so I can see what I'm doing wrong. Thank you.
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  2. #2
    Senior Member Pinkk's Avatar
    Joined
    Mar 2009
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    Uptown Manhattan, NY, USA
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    x=15+y

    2x+3y=2(15+y)+3y=90

    30+5y=90

    5y=60

    y=12

    x = 15+y=15+12=27

    Solution:

    x=27, y=12

    To check the solution:

    27-12=15

    2(27) + 3(12)=54+36=90
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  3. #3
    MHF Contributor
    Joined
    Mar 2007
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    1,240

    Talking

    Quote Originally Posted by complicated View Post
    I keep thinking I have it until I go back and check my answer, then I keep finding out I'm completely wrong....

    I really want to understand the steps involved so I can see what I'm doing wrong.
    Unfortunately, while the complete worked solution will of course allow you to see one "right" way of doing this, it won't help you "see what I'm doing wrong".

    To provide that service, we'll need to be able to see your work, so we can find, explain, and correct any errors.

    Thank you!
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