Final answer:
To find the chronological age of a person with a mental age of 30 and an IQ of 90, use the formula involving direct and inverse variation. The chronological age is approximately 33.33.
Step-by-step explanation:
To find the chronological age of a person with a mental age of 30 and an IQ of 90, we need to use the formula involving direct and inverse variation. The formula is given as:
IQ = k * (Mental Age / Chronological Age)
where IQ is the intelligence quotient, k is the constant of variation, Mental Age is the mental age of the person, and Chronological Age is the chronological age of the person.
Since we are given that the person has a mental age of 30 and an IQ of 90, we can substitute these values into the formula and solve for Chronological Age:
90 = k * (30 / Chronological Age)
To find the value of k, we can use the given information that a person with a mental age of 30 and a chronological age of 25 has an IQ of 120:
120 = k * (30 / 25)
Solving for k, we get:
k = 120 * (25 / 30) = 100
Now we can substitute the value of k into the first equation and solve for Chronological Age:
90 = 100 * (30 / Chronological Age)
Dividing both sides of the equation by 100 and rearranging, we get:
Chronological Age = 100 * (30 / 90) = 33.33
Therefore, the chronological age of a person with a mental age of 30 and an IQ of 90 is approximately 33.33.