The illumination provided by a car’s headlight varies inversely as the square of the distance from the headlight. If a headlight produces 15 footcandles at a distance of 20 feet, what will be the illumination at 40 feet? At 100 feet?

Answer 1

You are told that

I(d) = k/d^2

15 = k/400
k = 6000

I(40) = 6000/1600
I(100) = 6000/10000

Answer 2

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