Human blood can be classified into four common blood types—A, B, AB, and O. It is also characterized by the presence (+) or absence (–) of the rhesus factor. The table above shows the distribution of blood type and rhesus factor for a group of people. If one of these people who is rhesus negative (–) is chosen at random, the probability that the person has blood type B is `1/9` . What is the value of x ?

Answer

8

Explanation

In this group, `1/9`th of the people who are rhesus negative have blood type B. The total number of people who are rhesus negative in the group is 7 + 2 + 1 + x, and there are 2 people who are rhesus negative with blood type B. Therefore , `2/((7+2+1+x))=1/9`. Combining like terms on the left-hand side of the equation yields `2/((10+x))=1/9`. Multiplying both side of this equation by 9 yields `18/((10+x))=1`, and multiplying both sides of this equation by (10+x) yields 18 = 10 + x. Subtracting 10 from both sides of this equation yields 8 = x.