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Mobile ad spending. The amount spent worldwide in advertising on mobile devices can be estimated by f(x) =0.4x^2+0.01x+0.9. Where x is the number of years after 2005 and f(x) is in billions of dollars. When will worldwide mobile ad spending reaches $41 billion?

  • Math Help -

    solve 41 = .4x^2 + .01x + .9
    multiply by 100
    40x^2 + x + 90 = 4100
    40x^2 + x - 4010 = 0
    x = (-1 ± √641601)/80 = 10 or a negative

    it will take 10 yrs

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