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Math Help - SAT fractions

  1. #1
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    SAT fractions

    Hi, I was doing some problems in an SAT math workbook and came across this:
    (all parentheses added by me to deter confusion)
    1/(1+1/b) = p Which expression is 2p?
    The answer given by the book is 1/ ((1/2)+(1/2b))

    However, it would seem to me if p=1/(1+1/b) then 2p=2(1/(1+1/b)) = 2/(2(1+1/b)) = 2/(2+2/b)

    Can someone explain this to me please?
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  2. #2
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    Quote Originally Posted by ladymoon View Post
    Hi, I was doing some problems in an SAT math workbook and came across this:
    (all parentheses added by me to deter confusion)
    1/(1+1/b) = p Which expression is 2p?
    The answer given by the book is 1/ ((1/2)+(1/2b))

    However, it would seem to me if p=1/(1+1/b) then 2p=2(1/(1+1/b)) = 2/(2(1+1/b)) = 2/(2+2/b)

    Can someone explain this to me please?
    2p = \frac{p}{\frac{1}{2}} = \frac{1}{\frac{1}{2}} \cdot p =  \frac{1}{\frac{1}{2}} \cdot \frac{1}{1 + \frac{1}{b}} = \frac{1}{\frac{1}{2} + \frac{1}{2b}}
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  3. #3
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    Thanks Skeeter for the reply. I understand now how the book got the answer 1/ ((1/2)+(1/2b)). But I still don't understand logically why if p = something that 2*p = 2*something doesn't work. I know I'm probably just missing something incredibly stupid, but I just don't get it.
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  4. #4
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    Quote Originally Posted by ladymoon View Post
    Thanks Skeeter for the reply. I understand now how the book got the answer 1/ ((1/2)+(1/2b)). But I still don't understand logically why if p = something that 2*p = 2*something doesn't work. I know I'm probably just missing something incredibly stupid, but I just don't get it.
    it works, but you did not work it correctly ...

    However, it would seem to me if p=1/(1+1/b) then 2p=2(1/(1+1/b)) = 2/(2(1+1/b)) = 2/(2+2/b)
    2 \cdot \frac{1}{1 + \frac{1}{b}} = \frac{2}{1 + \frac{1}{b}} , not \frac{2}{2 + \frac{2}{b}}<br />

    \frac{2}{2 + \frac{2}{b}} = p<br />
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  5. #5
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    I knew I was doing something stupid! It's 2/1 * 1/(1+1/b). Now can you explain to me why the answer is 1/(1/2+1/2b) not 2/(1+1/b). It's probably something stupid again, but I really appreciate the help.
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