The average age of $24$ boys and their teacher is $15 \,years.$ When the teacher's age is excluded, the average age decreases by $1\, year.$ The age of the teacher is in $years$ ?

The average salary per head of all the workers in a company is $Rs. \,95.$ The average salary of $15$ officers is $Rs.\, 525$ and the average salary per head of the rest is $Rs. \,85.$ Find the total number of workers in the workshop.

The sum of three numbers is $98 .$ If the ratio between the first and second is $2: 3$ and that between the second and the third is $5: 8$ , then the second number is

Of three numbers, the second is thrice the first and the third number is three-fourths of the first.If the average of the three numbers is $114,$ the largest number is

In a competitive examination, the average marks obtained was $45 .$ It was later discovered that there was some error in computerization and the marks of $90$ candidates had to be changed from $80$ to $50$ , and the average came down to $40$ marks. The total number of candidates appeared in the examination is 

The average of first three numbers is double of the fourth number. If the average of all the four numbers is $12,$ find the $4^{th}$ number.