Out of nine persons$, 8$ persons spent $Rs.\, 30$ each for their meals. The ninth one spent $Rs.\, 20$ more than the average expenditure of all the nine. The total money spent by all of them was (in $Rs.\,$)

The average of nine numbers is $50.$ The average of the first five numbers is $54$ and that of the last three numbers is $52 .$ Then the sixth number is?

The average expenditure of a man for the first five months is $Rs.\, 3600$ and for next seven months it is $Rs.\, 3900 .$ If he saves $Rs.\, 8700$ during the $year,$ his average income per $month$ is (in $Rs.$)

The average of $12$ results is $15,$ and the average of the first two is $14.$ What is the average of the rest?

Out of four numbers, whose average is $60,$ the first one is one-fourth of the sum of the last three. The first number is

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