The average age of a man and his two twin sons,born on the same day,is $30 \, \text{years}$. The ratio of the ages of the father and one son is $5:2$. What is the father's age in $\text{years}$?

There were $35$ students in a hostel. If the number of students increases by $7$,the expenses of the mess increase by $Rs. 42$ per day,while the average expenditure per head diminishes by $Rs. 1$. Find the actual expenditure of the mess (in $Rs.$).

The daily earnings of a taxi driver during a week are: $Rs. 60, Rs. 65, Rs. 70, Rs. 52.50, Rs. 63, Rs. 73,$ and $Rs. 68$. What is his average daily earning for the week (in $.50$)? (in $Rs.$)

The average marks of Sameer decreased by $1,$ when he replaced the subject in which he scored $40$ marks with two other subjects in which he scored $23$ and $25$ marks respectively. Later,he also included $57$ marks of Computer Science,and the average marks increased by $2.$ How many subjects were there initially?

The sum of three numbers is $98$. If the ratio between the first and second is $2:3$ and between the second and third is $5:8$,then the second number is:

David obtained $76, 65, 82, 67$ and $85$ marks (out of $100$) in English,Mathematics,Physics,Chemistry,and Biology. What is his average marks?