One's intelligence quotient, or IQ, varies directly as a person's mental age and inversely as that person's chronological age. A person with the mental age of 25 and a chronological age of 20 has an IQ of 125. What is the chronological age of a person with a mental age of 40 and an IQ of 80?

Question

gw2011 · Answer

The chronological age is 50.  Here is how I got the answer:

Let MA=Mental Age
Let CA=Chronological Age

(MA/CA)(100)=IQ

(40/CA)=80
(40)(100)=80(CA)
(40)(100)/80=CA
50=CA