SOLUTION: Average age of students of an adult school is 40 years. 120 new students whose average age is 32 years joined the school. As a result the average age is decreased by 4 years. Find

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Question 293812: Average age of students of an adult school is 40 years. 120 new students whose average age is 32 years joined the school. As a result the average age is decreased by 4 years. Find the number of students of the school after joining of the new students:
(a) 1200 (b) 120 (c) 360 (d) 240
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
let the number of students be x. The sum of all their ages = 40x
120 joined
total is x+120
The sum of all their ages = 40x+ 120*32
=40x + 3840
average age now is 36
40x+3840 / x+120 =36
40x+3820 = 36(x+120)
40x+3840 =36x + 4320
40x-36x= 4320-3840
4x= 480
x= 120
initially there were 120. 120 joined. so total isd 240 students