dse 2007 doubts

[Diyasini majumdar]

a primary school has 6 classses numbered 1 to 6 .class 1 has twice as many as students as each of the other  classses .wat is the probability that a randomly selected student is from a odd numbered class?


some1 pls help me wid dis one?

[Amit Goyal]

Ques. A primary school has 6 classses numbered 1 to 6. Class 1 has twice as many as students as each of the other  classes. What is the probability that a randomly selected student is from an odd numbered class?

Ans. Let the number of students in class 2 be n. Therefore, the number of students in class 1 is 2n and in classes 3 to 6, its n each.
Pr(randomly selected student is from an odd numbered class) = (2n+n+n)/(2n+5n) = 4/7