The average age of four members of a family is $32$ years. If the age of a guest is included,then the average age increases by $12.5 \%$. What is the age (in years) of the guest?

$A$ family consists of grandparents,parents,and three grandchildren. The average age of the grandparents is $67 \text{ years}$,that of the parents is $35 \text{ years}$,and that of the grandchildren is $6 \text{ years}$. What is the average age of the family? (in $\text{years}$)

The average weight of a group of $20$ boys was calculated to be $89.4 \, kg$ and it was later discovered that one weight was misread as $78 \, kg$ instead of $87 \, kg$. The correct average weight is (in $kg$).

The average of $6$ numbers is $20$. If one number is removed, the average becomes $15$. What is the number removed?

Average age of $A, B$ and $C$ is $84 \text{ years}$. When $D$ joins them,the average age becomes $80 \text{ years}$. $A$ new person,$E$,whose age is $4 \text{ years}$ more than $D$,replaces $A$ and the average of $B, C, D$ and $E$ becomes $78 \text{ years}$. What is the age of $A$ (in $\text{years}$)?

The average temperature of the first $4 \, \text{days}$ of a week is $38.6^{\circ} \text{C}$ and that of the last $4 \, \text{days}$ is $40.3^{\circ} \text{C}$. If the average temperature of the entire week is $39.1^{\circ} \text{C}$, find the temperature on the $4^{th} \, \text{day}$ (in $^{\circ} \text{C}$).