What is the average of the squares of the first $19$ natural numbers ?
$124$
$127.5$
$130$
$133.5$
The average of three numbers is $154 .$ The first number is twice the second and the second number is twice the third. The first number is
A batsman has an average of $30$ runs in his $42$ inning. The difference between his maximum and minimum score is $100 .$ If these two innings are removed his average for $40$ innings comes down to $28 .$ What is his minimum score?
The average monthly expenditure of a family for the first four months is $Rs.\, 2570$, for the next three months $Rs.\, 2490$ and for the last five months $Rs.\,3030.$ If the family saves $Rs.\, 5320$ during the whole $year,$ the average monthly income of the family during the year is (in $Rs.\,$)
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
The average age of $15$ students of a class is $15\, year.$ Oute of these, the average age of $5$ students is $14 \,year$ and that of the other $9$ students is $16\, year.$ The age of the $15^{th}$ students is? (in $year$)