The average of $6$ numbers is $8$. What is the $7^{th}$ number so that the average becomes $10$?

The average weight of $24$ students is $35\, kg$. If the weight of the teacher is added, the average increases by $400\, g$. What is the weight of the teacher in $kg$?

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 $\text{years}$):

The average age of four brothers is $12 \, \text{years}$. If the age of their mother is also included, the average increases by $5 \, \text{years}$. The age of the mother (in $\text{years}$) is:

If the average marks of three batches of $55, 60,$ and $45$ students are $50, 55,$ and $60$ respectively,then the average marks of all the students is:

The average age of Seema,Sapna,Asha,Kavita,and Atrye is $40 \text{ years}$. The average age of Seema and Sapna is $35 \text{ years}$,and the average age of Asha and Kavita is $42 \text{ years}$. What is the age of Atrye?