If the average age of 20 students in Class-I is 10 years and average age of 25 students in Class II is 12 years, find the average age (in years) of all students.
M is the largest 4 digit number, which when divided by 4, 5, 6 and 7 leaves remainder as 2, 3, 4, and 5 respectively. What will be the remainder when M is divided by 9?