Question

The following distribution shows the daily pocket allowance given to the children of a multistorey building. The average pocket allowance is Rs 18.00. Find the missing frequency.

Class:	11−13	13−15	15−17	17−19	19−21	21−23	23−25
Frequency:	7	6	9	13	−	5	4

Answer 1

Given: Mean = 18

Suppose the missing frequency is x.

Let the assumed mean A = 18 and h = 2.

We know that mean,

Now, we have,,.

Putting the values in the above formula, we have

$$\begin{gathered} 18=18+2\left(\frac{x-20}{x+44}\right) \\ \Rightarrow 2\left(\frac{x-20}{x+44}\right)=0 \\ \Rightarrow x-20=0 \\ \Rightarrow x=20 \end{gathered}$$

Thus, the missing frequency is 20.