Question

The average pocket money of a class is rs.100 , which has 100 students. If teachers pocket money is included, then the average pocket money becomes 105. Then what will be the pocket money of teacher.

Answer 1

Given :

The average pocket money of the  class  = Rs 100

The total number  of students in the class  whose pocket money is given = 100

New average pocket money when teachers pocket money is included = 105

To Find :

What is the pocket money of the teacher ?

Solution :

From the 1st case we have :

Average pocket money  = $\frac{sum \hspace3 of \hspace3 average \hspace3 pocket \hspace3 money \hspace3 of \hspace3 all \hspace3 students }{ no \hspace3 of \hspace3 students }$

So  , $100 = \frac{S}{100}$

Or , $S = 100 \times 100$

Let pocket of teacher be = x

So in next case again  we have :

105 = $\frac{S'}{101}$

Or, $S' = 105 \times 101$

Now S' = S + x   ( since it is included with teacher's pocket money ).

So , $x = S' - S$

         =$101 \times 105 - 100 \times 100$

         =10605 - 10000

         = 605

Hence average pocket money of teacher is Rs 605 .