The average marks of Sameer decreased by $1,$ when he replaced the subject in which he has scored $40 \,marks$ by the other two subjects in which he has just scored $23$ and $ 25$ marks respectively. Later he has also included $57$ marks of Computer Science, then the average marks increased by $2.$ How many subjects were there initially?

Average of $a, b$ and $c$ is $11 ;$ average of $c, d$ and $e$ is $17 ;$ average of $e$ and $f$ is $22$ and average of $e$ and $c$ is $17 .$ Find out the average of $a, b,$ $c , d , e$ and $f ?$

Three $years$ ago the average age of a family of $5$ members was $17\, years.$ With the birth of a new baby, the average remains the same three even today. Find out the age of the baby.(in $years$)

The average marks in English of a class of $24$ students is $56 .$ If the Marks of three students were misread as $44,45$ and $61$ in lieu of the actual marks $48,59$ and $67$ respectively, then what would be the correct average ?

Average age of $5$ boys is $16$ $year$ of which that of $4$ boys is $16\, year\, 3\, months.$ The age of the $5^{th}$ boy is

$10$ $years$ ago the average age of all the $25$ $teachers$ of the Girls college was $45\, years.$ $4 \,years$ ago, the principal has retired from her post at the age of $60 \,year.$ So after one year a new principal whose age was $54 \,years$ recruited from outside. The present average age of all the teachers is, if principal is also considered as a teacher