Aufgabe:
The illuminance of a surface varies inversely
with the square of its distance from the light
source. If the illuminance of a surface is
120 lumens per square meter when its distance
from a certain light source is 6 meters, by how
many meters should the distance of the surface
from the source be increased to reduce its
illuminance to 30 lumens per square meter?
(A) 3
(B) 6
(C) 12
(D) 15
(E) 18
Problem/Ansatz:
