The average marks of $120$ students are $35.$ If the average of passed students was $39$ and failed students was $15,$ then find the number of students who have passed.

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

With an average speed of $40 \, km/h$,a train reaches its destination on time. If it goes with an average speed of $35 \, km/h$,it reaches late by $15 \, \text{minutes}$. The total journey is (in $km$):

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

The average of certain first consecutive natural numbers is $20.5$. Find their sum.

The average weight of $36$ students is $50 \,kg$. It was found later that the figure of $37 \,kg$ was misread as $73 \,kg$. What is the correct average? (in $kg$)