Out of $30$ teachers of a school, a teacher of age $60$ $years$ retired. In his place another teacher of age $30$ $years$ was appointed. As a result, the mean age of the teachers will
remain same
decrease by $2$ years
decrease by $6$ months
decrease by $1$ year
The batting aterage for $40$ innings of a cricketer is $50$ nuns. His highest score exceeds his lowest score by $172$ runs. If these two innings are excluded, the average of the remaining $38$ innings is $48$ runs. The highest score of the player is
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 of the test scores of a class of $'m'$ students is $70$ and that of $'n'$ students is $91.$ When the scores of both the classes are combined, the average is $80 .$ What is $n / m$ ?
If the mean of $a, b, c$ is $M$ and $a b+b c+c a=0,$ then the mean of $a^{2}, b^{2}, c^{2}$ is
A motorist covered the first $20\, km$ of his journey in 30 mifitutes and the remaining $29\, km$ in $40\, minutes$. His average speed in $km / hr$ is: