10. The age of a government substitute legislator is equal to his IQ. If he joins the cabinet, he will increase the average age of the cabinet members from 50 years to 51 years, and decrease the IQ from 114 to 111. Then, after he joins, the number of cabinet members is ( ).
(A) 12
(B) 15
(C) 20
(D) 30
(E) None of the above answers is correct
10. (B) Let the age and IQ of the substitute member be $x$, and the number of cabinet members be $n$, then $x-51=n(51-50)$, and $111-x$ $=n(114-111)$, adding the two equations gives $60=4 n$.