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

The sum of five numbers is $260 .$ The average of the first two numbers is $30$ and the average of the last two numbers is $70 .$ What is the third number ?

$19$ persons went to a hotel for a combined dinner party. $13$ of them spent $Rs.\, 79$ each on their dinner and the rest spent $Rs.\, 4$ more than the average expenditure of all the $19 .$ What was the total money spent by them.

The average weight of $10$ students is increased by half a $kg$ when one of the students weighing $50\, kg$ is replaced by a new student. Find out the weight of the new student.(in $kg$)

The average of $5$ quantities is $6 .$ The average of three of them is $8 .$ What is the average of remaining two quantities?

The average of $7$ numbers is $5 .$ If the average of first six of these numbers is $4,$ the seventh number is