Question

average age of 3 children is 9 year which get doubled if fathers age is included.what is the father age
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Answer 1

Average age = 9 years

Number of children = 3

So sum of ages of all the children = 3 X 9 = 27 years.

Average after the father's age was added = 18 years

So the sum of ages including father = 18 X 4 = 72years

Age of father = sum of ages including father - sum of ages of all children

                      = 72 - 27 = 45

So the age of father =  45 years.