The average marks of a student in four subjects is $75$. If the student obtained $80$ marks in the $5^{th}$ subject,then the new average is?

$A$ cyclist goes from one place to another and returns by the same route. He pedals his way uniformly with speed $u$ while going and with speed $v$ while returning. The average speed of his journey is

The average of marks of $28$ students in Mathematics was $50$. $8$ students left the school,then this average increased by $5$. What is the average of marks obtained by the students who left the school?

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 $Rs.$).

The total marks obtained by a student in Physics,Chemistry and Mathematics together is $120$ more than the marks obtained by him in Chemistry. What is the average marks obtained by him in Physics and Mathematics together?

Average age of $15$ students of a class is $15 \text{ years}$. Out of these,the average age of $5$ students is $14 \text{ years}$ and that of the other $9$ students is $16 \text{ years}$. The age of the $15^{th}$ student is (in $\text{years}$):