Question 797491
 The intensity I of light varies inversely as the square of the distance D from the source.
 If the intensity of illumination on a screen 5 ft from a light is 4 foot candles,
let k = constant, then I = {{{k/D^2}}}
Find K
{{{k/5^2}}} = 4
k = 25*4
k = 100
:
find the intensity on a screen 20ft from the light. 
I = {{{100/20^2}}}
I = {{{100/400}}}
I = {{{1/4}}} foot candle