Question

a man had seven children. when their average age was 12 years a child aged 6 years was lost. find the average age of the remaining 6 children.

Answer 1

heir average age was 12 years
THERE ARE 7 CHILDREN
SO x/7=12
x=12*7
x= 84
so sum of their ages is  84

child aged 6 years was lost.
average of remaiing=[84-6/6]
                                =13 years 


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Answer 2

Given :

The number of children that a man had = 7

The average age of 7 children = 12

At average of 12 , one child aged 6 years wad lost

To Find :

The average age of the remaining 6 children

Solution :

Let The average age of the remaining 6 children = A years

∵  The average age of 7 children = 12

i.e  $\dfrac{x_1+x_2+x_3+x_4+x_5+x_6+x_7}{7}$  = 12

Or,  $x_1+x_2+x_3+x_4+x_5+x_6+x_7$ = 12 × 7

Or, $x_1+x_2+x_3+x_4+x_5+x_6+x_7$ = 84

Again

At average of 12 , one child aged 6 years wad lost

So,  $x_1+x_2+x_3+x_4+x_5+x_6+6$ = 84

or,  $x_1+x_2+x_3+x_4+x_5+x_6$ = 84 - 6

i.e $x_1+x_2+x_3+x_4+x_5+x_6$ = 78

So, The  average age of the remaining 6 children = $\dfrac{x_1+x_2+x_3+x_4+x_5+x_6}{6}$

Or ,  A = $\dfrac{78}{6}$

i.e Average of 6 children = A = 13 years

Hence, The  average age of the remaining 6 children is 13 years  Answer