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.

Answer 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

Answer 2

How did you get 25?