<PRE><B>Question 891485</B>
The average age of 30 boys in a class is 13 years ,
 9 more boys whose average age is 15 years join the class.
 Find the average of the whole class?
:
That is a total of 39 boys divided into two groups
Av = {{{((30(13)+9(15)))/39}}}
Av = {{{((390+135))/39}}}
Av = 525/39
Av = 13.5 av of the whole class
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