The mean marks of $10$ boys in a class is $70 \%$,whereas the mean marks of $15$ girls is $60 \%$. The mean marks of all the $25$ students is

The average salary of all the workers in a workshop is $Rs. 8000$. The average salary of $7$ technicians is $Rs. 12000$ and the average salary of the rest is $Rs. 6000$. The total number of workers in the workshop is

The average speed of a train in the onward journey is $25\%$ less than that of the return journey. The train halts for one hour on reaching the destination. The total time taken for the complete to and fro journey is $17\, \text{hours}$,covering a distance of $800\, \text{km}$ (one way). The speed of the train in the onward journey is (in $\text{km/h}$):

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 $kg$)

In a $20$ over match,the required run rate to win is $7.2$. If the run rate is $6$ at the end of the $15^{th}$ over,the required run rate to win the match is

Three years ago,the average age of a family of $5$ members was $17$ years. $A$ baby having been born,the average age of the family is the same today. The present age of the baby is (in years):