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4.Average
hard
Three years ago, the average age of a family of $5$ members was $17\, years.$ A baby having been born, the average age of the family is the same today. The present age of the baby is (in $years$)
A
$1$
B
$1 \frac{1}{2}$
C
$2$
D
$3$
Solution
Average of age of family of $5$ members $(3$ years ago) $=17$ years
$\therefore$ Present age of family of $6$ members with a new born baby $=17$ year
Let the age of baby be $x$
$\frac{(17+3) \times 5+x}{6}=17$
$\frac{100+x}{6}=17$
$100+x=102$
$x=2$ years
Standard 13
Quantitative Aptitude