Of the three numbers, the average of the first and the second is greater than the average of the second and the third by $15 .$ What is the difference between the first and the third of the three numbers?

A student finds the average of $10,2$ digit numbers. If the digits of one of the number is interchanged, the average increases by $3.6 .$ The difference between the digits of the $2 -$digit numbers is

Amitabh's average expenditure for the $January$ to $June$ is $Rs.\, 4200$ and he spends $Rs.\, 1200$ in $January$ and $Rs. \,1500$ in $July.$ The average expenditure for the month of $February$ to $July$ is (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

The average monthly income of $P$ and $Q$ is $Rs.\,5050.$ The average monthly income of $Q$ and $R$ is $Rs.\,6250$ and the average monthly income of $P$ and $R$ is $Rs.\,5200.$ The monthly income of $P$ is

Find average of all prime numbers between $60$ and $90.$