The average age of $30$ women decreases by $3$ months if a new person,Neha,is included in place of a $25$ year old woman. Calculate the age of Neha in years.

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?

What is the average of all numbers between $100$ and $200$ which are divisible by $13$ (in $.5$)?

$A$ person travels $\frac{1}{3}$ of his journey by bus at $60\, km/h$,$\frac{1}{3}$ by scooter at $30\, km/h$,and the rest by walking at $10\, km/h$. Find his average speed for the whole journey (in $km/h$).

The mean weight of $150$ students in a class is $60 \, kg$. The mean weight of boys is $70 \, kg$ and that of girls is $55 \, kg$. What is the number of boys in the class?

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?