Math

the intensity l of light from a light bulb, measured in watts per square meter (w/m^2), varies inversely as the square of the distance d from the light bulb. Suppose l is 70 w/m^2 when the distance is 5m. Find the intensity when the distance from the light bulb is 4 m away.

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  1. I = k (1/d^2)
    given: when I = 70, d = 5
    70 = k/25
    k = 1750

    so I = 1750/d^2

    when d = 4
    I = 1750/4^2 = 109.375

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  2. How did you get 25?

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