each employee of company x is a member of precisely 1 of 3 shifts of employees . among the 60 members of the first shift , 20 percent participate in the pension program ; among the 50 members of the second shift , 40 percent participate in the pension program ; and among the 40 members of the third shift , 10 percent participate in the pension program . what percent of the workers at company x participate in the pension program ?