What will be the average of even numbers between $11$ and $63$?

The sum of the ages of father and son at present is $33 \, \text{years}$. Two years ago, the product of their ages was $28 \, \text{years}$. What is the age of the father and the son (in $\text{years}$)?

The average of marks obtained by $120$ candidates in a certain examination is $35$. If the average marks obtained by passed candidates are $39$ and those of the failed candidates are $15$,then what is the number of candidates who passed the examination?

The average temperature from Monday to Thursday is $48^{\circ}C$ and from Tuesday to Friday is $52^{\circ}C$. If the temperature on Monday is $42^{\circ}C$,what was it on Friday? (in $^{\circ}C$)

The daily maximum temperature in Delhi,for $7$ consecutive days in $May, 1988$,were $42.7^{\circ} C, 44.6^{\circ} C, 42.0^{\circ} C, 39.1^{\circ} C, 43.0^{\circ} C, 42.5^{\circ} C$ and $38.5^{\circ} C$. Find out the average daily maximum temperature (in $^{\circ} C$).

$A$ car owner buys petrol at $Rs. 7.50$,$Rs. 8$,and $Rs. 8.50$ per litre for three successive years. What is the approximate average cost per litre of petrol if he spends $Rs. 4000$ each year?