A student finds the average of ten $2 -$digit numbers. While copying numbers, by mistake, he writes one number with its digits interchaged. As a result his answer is $1.8$ less than the correct answer. The diference of the digits of the number, in which he made mistake, is

A batsman makes a score of $8$ runs in the $16^{\text {th }}$ match and thus increases his average runs per match by $3 .$ What is his average after the $16^{\text {th }}$ match?

A man spends on an average $Rs.\, 269.47$ for the first $7 \,months$ and $Rs.\, 281.05$ for the next $5\, months.$ Find out his monthly salary if he saved $Rs.\,308.46$ during the $year.$ (in $Rs.$)

What is the average of first $7$ multiples of $7\, ?$

The average age of a committee of $8$ members is $40 \,years.$ A member, aged $55\, years,$ retired and he was replaced by a member aged $39\, years.$ The average age of the present committee is (in $years$) 

The average age of $8$ men is increased by $2\,years$ when two of them whose ages are $21\, years$ and $23\, years$ are replaced by two new men. The average age of the two new men is