Question

there ara 40 boys in class 8 and their average age is 14 years. Also, there are 35 boys in class 9 and their average age is 15 years. find the average age of both the classes.

Answer 1

AVERAGE =SUM OF THE OBSERVATIONS /TOTAL NO. OF OBSERVATIONS

15+35/2  = 50/2

=25

Answer 2

We calculate average by( sum of observation divided by the no. of observation) so in class 8 {let the sum of ages of boys is x}

So, x/40=14

x=40*14[as anything on LHS is in denominator when taken at RHS then it is multiplied by the terms of RHS ]

x=560

Now,

Similarly

y=35*15[let the sum of students of class 9]

y=525

Now the average of height of student of classes is equal to the sum of height of the both classes divided by no.of students in both classes .

So,

(x+y)/75

(525+560)/(35+40)

=1085/75

=14.666666667