The average age of 120 members of a society is 62.5 years. By addition of 30 new members, the average age becomes 58.2 years. What is the average age of the newly joined members?

41 years 

ATQ,

Sum of ages of 120 members of society = 120 x 62.5 = 7500

Sum of ages when new 30 members are added = 150 x 58.2 = 8730

Sum of ages of 30 new members = 8730 - 7500 = 1230

Average age of 30 newly joined members = 41 years