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Math Help - help with algebra formula

  1. #1
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    Oct 2009
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    help with algebra formula

    Hi,

    I'm having difficulty with this formula.

    12%=kei+((1-0.3)x(kei-4%)x(20/80))

    I need to find the value of kei. The book I am working with tells me the answer is 10.8% but I can't work out how you get to that answer.

    Any assisstance would be greatfully appreciated?
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  2. #2
    Super Member
    Joined
    Jan 2009
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    Quote Originally Posted by mirimiri376 View Post
    Hi, I'm having difficulty with this formula.

    12%=kei+((1-0.3)x(kei-4%)x(20/80))

    I need to find the value of kei. The book I am working with tells me the answer is 10.8% but I can't work out how you get to that answer.
    Any assisstance would be greatfully appreciated?
    Given: 12%=kei+((1-0.3)x(kei-4%)x(20/80))

    Change % to decimal value
    0.12 = kei + ( 0.70 x(kei-0.04)x(0.25))

    some rearrangement
    0.12 = kei + (kei-0.04)x(0.25x0.70)

    reduction
    0.12 = kei + (kei-0.04)x(0.175)

    expand & simplify
    0.12 = kei + 0.1750kei - 0.007
    0.12 + 0.007 = 1.175kei
    0.127/1.175 = kei

    0.127/1.175 = 0.108085 = 10.8% = kei

    .
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