The intensity of light received at a source varies inversely as the square of the distance from the source. A particular light has an intensity of 20 foot-candles at 15 feet. What is the lights intensity at 10 feet?
We can solve this problem in two ways, either solving for k and subbing back in or by using ratios to eliminate k. In many common inverse square dependences k can be quite a lot of constants and ratios often save on calculation time. We will use both here though.