Out of seven given numbers,the average of the first four numbers is $4$ and that of the last four numbers is also $4$. If the average of all the seven numbers is $3,$ then the fourth number is?

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 $^{\circ} C$).

The average of marks obtained by $100$ candidates in a certain examination is $30$. If the average marks of passed candidates is $35$ and that of the failed candidates is $10$,what is the number of candidates who passed the examination?

The average marks obtained by $180$ students in an examination is $50$. If the average marks of passed students is $80$ and the average marks of failed students is $40$,then what is the number of students who failed the examination?

The average age of $10$ men is increased by $2 \, \text{years}$ when one of them, aged $25 \, \text{years}$, is replaced by a new man. What is the age of the new man (in $\text{years}$)?

The average of ten numbers is calculated. If each number is increased by $12 \%$,then the average