IQ stands for Intelligence Quotient, which is a number that represents how intelligent a person is. It is calculated by comparing a person’s mental age (MA) with their chronological (actual) age (CA) using the following formula: IQ = MA/CA ×100 Mental age is calculated by giving tests to thousands of people of different ages, this makes it possible to see how the average 12 year old, for example, performs on the test. Someone who performs at the same level as a 12 year old would have a mental age of 12. Likewise, someone who performs at the same level as a 24 year old would have a mental age of 24. Applying the formula: if a 12 year old has a mental age of 12 they have a normal IQ of 100, but a 24 year old with a mental age of 12 would have an IQ of 50 and would be considered to have learning difficulties.