Find average of all prime numbers between $60$ and $90.$
$72$
$74.7$
$74$
$73.6$
A family consists of grand parents, parents and three grand children. The average age of the grand parents is $67\, years,$ that of the parents is $35\, years$ and that of the grand children is $6 \,years.$ What is the average age of the family? (in $years$)
The average score of Rahul, Manish and Suresh is $63.$ Rahul's score is $15$ less than Ajay and $10$ more than Manish. If Ajay scored $30$ marks more than the average score of Rahul, Manish and Suresh, what is the sum of Manish's and Suresh's scores ?
The mean of $100$ items was $46 .$ Later on it was discovered that an item $16$ was misread as $61$ and another item $43$ was misread as $34 .$ It was also found that the number of items twas $90$ and not $100 .$ Then what is the correct mean?
The average marks in English subject of a class of $24$ students is $56 .$ If the marks of three students were misread as $44,45$ and $61$ of the actual marks $48,59$ and $67,$ respectively, then what would be the correct average?
The arithmetic mean of $100$ observations is $24.6$ is added to each of the observations and, then each of them is multiplied by $2.5 .$ Find the new arithmetic mean.