eight-year-old harvey has a mental age of four. what is his intelligence quotient?

Computation of intelligence quotient is mental age/chronological age (real age)*100.

Harvey is 8 years old (Chronological age)
                 4 years old (mental age)

               =(4/8)*100
               = 0.5*100
               =50  intelligence quotient 

Based on Binet's scale 70% and below belongs to the cluster of below normal IQ levels and Harvey is included in this cluster. 

Yes all of them are right

To sum it up you’ll get in a lot of trouble and even some legal action can be taken