There was one mess for $30$ boarders in a certain hostel. On the number of boarders being increased by $10,$ the expenses of the mess were increased by $Rs.\,40$ per month while the average expenditure per head diminished by $Rs.\,2.$ Find out actual monthly expenses. (in $Rs.$)

There are two groups $A$ and $B$ of a class, consisting of $42$ and $28$ students, respectively. If the average weight of group $A$ is $25 \,kg$ and that of group $B$ is $40 \,kg ,$ find the average weight of the whole class.

On $24^{\text {th }}$ May, 2008 the maximum temperature of Delhi, Kollkata and Mumbai were recorded as $35^{\circ} C$, $33^{\circ}$ and $34^{\circ} C$ respectively. What was the maximum temperature of Chennai so that the average maximum temperature of those cities would be $35^{\circ} C$ (in $^{\circ} C$ )

The average of $25$ results is $20 .$ the average of first $12$ results is $15$ and that of the last $12$ results is $18 .$ Then, the $13^{ th}$ results is

The average of three numbers is $28 .$ If first number is half of the second and the $3^{rd}$ number is twice the second, then the third number is?