In a survey of 30 consumers of detergents, 5 people said they
are loyal to brand A, while another 5 are loyal to brand B. Five
surveyed said they do not use either brands A, B, nor C, but use
some other detergents not included in the survey. A total of ten
consumers said they prefer brand A, and a total of 11 said they
prefer brand C. Four said they are using both A and B. There were
no one who used both brands B and C. Further, almost peculiarly, no
one said they used A, B, and C simultaneously.
a. How many person uses brand A or brand B but not brand C?
b. How many person uses both brand A and brand C?