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Question 81
The average age of 120 members of a society is 60.7 years. By addition of 30 new members, the average age becomes 56.3 years. What is the average age (in years) of newly joined members?
Solution
Average age of 120 members of the society = 60.7 years
=> Total age of 120 members = $$120\times60.7=7284$$ years
Let the average age of 30 new members = $$x$$ years
=> Total age of the 30 members = $$30x$$ years
According to ques, new average = 56.3 years
=> $$\frac{7284+30x}{(120+30)}=56.3$$
=> $$7284+30x=56.3\times150=8445$$
=> $$30x=8445-7284=1161$$
=> $$x=\frac{1161}{30}=38.7$$
=> Ans - (D)
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