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 arithmetic mean of the scores of a group of students in a test was $52$. The brightest $20\%$ of them secured a mean score of $80$ and the dullest $25\%$ a mean score of $31$. The mean score of the remaining $55\%$ is

The average income of $A$ for $15$ days is $Rs. 70$. The average for the first five days is $Rs. 60$ and that for the last nine days is $Rs. 80$. $A$'s income for the sixth day is (in $Rs.$):

The average weight of $45$ students in a class is $52 \, kg.$ Five of them whose average weight is $48 \, kg$ leave the class and other $5$ students whose average weight is $54 \, kg$ join the class. What is the new average weight (in $kg$) of the class?

The average weight of $24$ students in section $A$ of a class is $58 \,kg,$ whereas the average weight of $26$ students in section $B$ of the same class is $60.5 \,kg$. Find out the average weight of all the $50$ students of the class. (in $kg$)

In a cricket team of $11$ boys,one player weighing $42 \,kg$ is injured and replaced by another player. If the average weight of the team is increased by $100 \,g$ as a result of this,then what is the weight of the new player (in $.1$)? (in $kg$)