The average of prime numbers between $1$ and $20$ is

The average weight of five persons sitting in a boat is $38\, kg$. The average weight of the boat and the persons sitting in the boat is $52\, kg$. What is the weight of the boat (in $kg$)?

The average height of the students of a class of $20$ is $105 \, cm$. If ten more students of average height of $120 \, cm$ join this class,the average height of the class will become (in $cm$)?

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

Visitors to a show were charged $Rs. 15.00$ each on the first day,$Rs. 7.50$ on the second,and $Rs. 2.50$ on the third day. The total attendance of visitors for the three days was in the ratio $2:5:13$. Find the average charge per visitor for the entire show (in $Rs.$).

$A$ cricketer whose bowling average is $12.4$ runs per wicket takes $5$ wickets for $26$ runs and thereby decreases his average by $0.4$. The number of wickets taken by him till the last match was: