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 was $90$ and not $100 .$ Then, what is the correct mean?

Average age of $A, B$ and $C$ is $84\, years.$ When $D$ joins them the average age becomes $80\, years.$ A new person, $E,$ whose age is $4 \,years$ more than $D,$ replaces $A$ and the average of $B, C, D$ and $E$ becomes $78\, years.$ What is the age of $A$ ? (in $years$)

The average salary of workers in $AMS$ careers is $Rs.\, 2,000$ , the average salary of faculty being $Rs. \,4,000$ and the management trainees being $Rs. \,$ $1,250 .$ The total number of workers could be

The average of five consecutive even numbers starting with $4,$ is

The average age of $8$ members of a group is $40 \,years.$ The age of $1$ member is $55\, years.$ After his retirement a new member comes in his place of age $39 .$ What is the effect of his retirement on the average age of group ?

The average of first three numbers is double of the fourth number. If the average of all the four numbers is $12,$ find the $4^{th}$ number.