The mean of marks secured by 30 students in division-A of class X is 67, 55 students of division-B is 63 and that of 40 students of division-C is 61. What is the mean of marks of the students of three divisions of Class X?
Among three numbers, the first is twice the second and thrice the third. If the average of three numbers is 396, then what is the difference between the first and the third number?