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The average of 31 persons of a group is 19 years. If a person is excluded, the average becomes 18 years. Find the age of excluded person.

Solution

Simple method :

Sum of the ages of 31 persons $=31 \times 19=589$ years

Sum of the ages of 30 persons $=30 \times 18=540$ years

$\therefore$ The age of excluded person $=589-540=49$ years; Ans.

Trick:

Required age

$$\begin{array}{l} =19-\frac{31-1}{1} \times(18-19) \\ =19+30 \times 1=49 ; \text { years; Ans. } \end{array}$$

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