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Math Help - PLZ HELP!!!!

  1. #1
    Newbie
    Joined
    Sep 2008
    Posts
    9

    PLZ HELP!!!!

    the amount of light as you go deeper into a lake is given by the formula L/100=(0.9)^5d, where d is the depth below the surface,in metres, and L is the percentage of the amount of light at the surface of the lake.
    find the value of L when
    a) d=1.4
    b) d=2.7
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  2. #2
    Junior Member
    Joined
    Oct 2008
    Posts
    35
    L = 100*(0.9)^5d

    a) substitute value d = 1.4

    then L = 100*(0.9)^7

    by logs

    log (.9)^7 = 7log .9 = -.3203
    get antilog = .478

    so L = 100* .478 = 47.8

    similarly for b)
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