The average marks of Sameer decreased by $1,$ when he replaced the subject in which he has scored $40 \,marks$ by the other two subjects in which he has just scored $23$ and $ 25$ marks respectively. Later he has also included $57$ marks of Computer Science, then the average marks increased by $2.$ How many subjects were there initially?

The average salary, per head, of all the workers of an institution is $Rs.\, 60 .$ The average salary of $12$ officers is $Rs.\, 400$; the average salary, per head, of the rest is $Rs.\,56.$ The total number of workers in the institution is

Nine friends have a dinner in a hotel. Eight of them spent $Rs.\, 12$ each on their meals and the ninth spent $Rs. \,16$ more than the average expenditure of all the nine. Find out the total money in $Rs.$ spent by them?

A library has an average of $510$ $visitors$ on Sundays and $240$ on other days. The average number of visitors per day in a month of $30 \,days$ beginning with a Sunday is 

The average of marks obtained by $150$ candidates in a certain examination is $50 .$ If the average marks of passed candidates is $55$ and that of the failed candidates is $25,$ what is the number of candidates who passed the examination?

Out of four numbers, whose average is $60,$ the first one is one-fourth of the sum of the last three. The first number is