The number of male employees in a certain unit is twice the number of female employees, the average age of male employees is 31 years old, and the average age of female employees is 40 years old. May I ask: What is the average age of all employees in this unit?
某单位男职工人数是女职工人数的2倍，男职工的平均年龄是31岁，女职工的平均年龄是40岁．请问：该单位全体职工的平均年龄是多少岁？
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