Re: Please Help!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

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Posted by Subhotosh Khan on October 11, 2002 at 13:40:05:

In Reply to: Please Help!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! posted by Jmiah on October 11, 2002 at 11:28:04:

: OK, here's the problem. I got one answer, my book got a different answer, and my calculator says both are wrong. Here's the equation:
Assuming the actual problem is
1/(8*x)-1/(7*x)=2, solve for x
: 1/8x-1/7x=2, solve for x

: I got:
: 7/56x-8/56x=2
: -1/56x=2
: -56x^-1=2 this should be (1/56)*x^(-1)=2
: -28x^-1=1
: x=28

: The book got:
: [1/7x-1/8x=2]56
: 7-8=112x this should be 8/x - 7/x = 112
: -1=112x
: x=-1/112

: My calculator got:
: 1/8x-1/7x=2, x=-112 (using q solver), when I substituted -112 for x, it came out equaling 2
: (1/{8[-112]}-1/{7[-112]}=2).

: I know the calculator is right, and I did find a way to get that answer, and I also see how I got my answer and the book got its answer, but I can't figure out what the book, or I, did wrong.
: P.S. those are one-eighth and one-seventh x.
: :-)

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Re: Please Help!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Subhotosh Khan 13:42:59 10/11/02 (0)

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: : OK, here's the problem. I got one answer, my book got a different answer, and my calculator says both are wrong. Here's the equation: : Assuming the actual problem is : 1/(8*x)-1/(7*x)=2, solve for x : : 1/8x-1/7x=2, solve for x : : I got: : : 7/56x-8/56x=2 : : -1/56x=2 : : -56x^-1=2 this should be (1/56)*x^(-1)=2 : : -28x^-1=1 : : x=28 : : The book got: : : [1/7x-1/8x=2]56 : : 7-8=112x this should be 8/x - 7/x = 112 : : -1=112x : : x=-1/112 : : My calculator got: : : 1/8x-1/7x=2, x=-112 (using q solver), when I substituted -112 for x, it came out equaling 2 : : (1/{8[-112]}-1/{7[-112]}=2). : : I know the calculator is right, and I did find a way to get that answer, and I also see how I got my answer and the book got its answer, but I can't figure out what the book, or I, did wrong. : : P.S. those are one-eighth and one-seventh x. : : :-) : ******************************** : : If the problem is : 1/8 * x - 1/7 * x = 2 (as stated, this is CORRECT interpretation - mult/Div before add/sub and left to right for equal hierchy) : x/8 - x/7 = 2 : 7x - 8x = 112 [Book's method] : -x = 112 : x = -112 : You really need to pay attention to hierchy of mathematical operations and parentheses. :

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