What is the average of the squares of the first $19$ natural numbers?

There were $35$ students in a hostel. If the number of students is increased by $7$,the expenditure on food increases by $Rs. \,42$ per day,while the average expenditure per student is reduced by $Rs. \,1$. What was the initial total expenditure on food per day? (in $Rs.$)

An aeroplane travels $2500 \, km$,$1200 \, km$,and $500 \, km$ at $500 \, km/h$,$400 \, km/h$,and $250 \, km/h$ respectively. The average speed is (in $km/h$):

Roshan bought $5$ pants at $Rs. 25$ each,$10$ shirts at $Rs. 50$ each,and $15$ ties at $Rs. 35$ each. Find the average price of all the articles in $Rs.$

Last year,$5$ companies had an average of $16$ non-working days each. If $3$ companies had $16$ non-working days each and $2$ companies had $5$ fewer non-working days each,what was the average number of non-working days for these $5$ companies last year?

The average salary of $20$ workers in an office is $Rs. 1900$ per month. If the manager's salary is added,the average becomes $Rs. 2000$ per month. The manager's annual salary (in $Rs.$) is