$A$ student finds the average of $10$ two-digit numbers. If the digits of one of the numbers are interchanged,the average increases by $3.6$. The difference between the digits of that two-digit number is:

The average weight of $15$ oarsmen in a boat is increased by $1.6\, kg$ when one of the crew,who weighs $42\, kg$,is replaced by a new man. Find the weight of the new man (in $kg$).

The average monthly expenditure of a family for the first four months is $Rs. 2750$,for the next three months is $Rs. 2940$,and for the last five months is $Rs. 3130$. If the family saves $Rs. 5330$ throughout the year,find the average monthly income of the family for that year (in $Rs.$).

Ashish has earned an average of $4200$ dollars for the first eleven months of the year. If he justifies his staying on in the $US$ on the basis of his ability to earn at least $5000$ dollars per month for the entire year,how much should he earn (in dollars) in the last month to achieve his required average for the whole year?

The average income of $A$ for $15$ days is $Rs. 70$. The average for the first five days is $Rs. 60$ and that for the last nine days is $Rs. 80$. $A$'s income for the sixth day is (in $Rs.$):

$A$ batsman,in his $12^{th}$ innings,makes a score of $63$ runs and thereby increases his average score by $2.$ The average of his score after $12^{th}$ innings is