A batsman scores $87$ runs in the $21^{st}$ match of his career. His average runs per match increase by $2.$ What is his average before the $21^{st}$ match?

The average of $13$ results is $50 .$ If the average of first $7$ results is $52$ and that of last $7$ results is $49,$ find the $7^{th}$ result.

A man spends on an average $Rs.\, 269.47$ for the first $7 \,months$ and $Rs.\, 281.05$ for the next $5\, months.$ Find out his monthly salary if he saved $Rs.\,308.46$ during the $year.$ (in $Rs.$)

The average marks obtained by $40$ students of a class is $86 .$ If the $5$ highest marks are removed, the average reduces by one mark. The average marks of the top $5$ students is

The average speed of a cyclist who covers first, second and third km at $20,16$ and $12\, km / hr$ respectively ( in $km / hr )$ is

The average age of students of a class is $15.8$ $years.$ The average age of boys in the class is $16.4\, years$ and that of the girls is $15.4 \,years.$ The ratio of the number of boys to the number of girls in the class is