Question 1110115
There are 24 students in a class.
 A student whose age is 18 years left the class.
 And his place is filled with another student.
 The average of the class was nearly lowered by 1 month.
 The age of new student is?
:
Let t = total of 23 student in months
then
{{{(t+12(18))/24}}} = the original average of the students in months
x = age of the new student in months
Original av - new student av = 1 month
{{{(t+216)/24}}} - {{{(t+x)/24}}} = 1 
multiply by 24, cancel the denominator
t + 216 - (t + x) = 24
t + 216 - t - x = 24
T's drop out
216 - x = 24
216 - 24 = x
192 = x
x = 192 months is the age of the new student therefore
192/12 = 16 yrs is the age of the new student in years.