The number of students in each of 10 different classes is a different

(1) The median number of students is equal to the mean number of students in the 10 classes.
The mean and median satisfying the above constraint can be 67,69,71,73,75,77,79 (since the numbers are at even consecutive difference)
There are 7 set possible, hence the standard deviation will vary as well.
(Insufficient)


(2) The number of students in any class is more than 63 and the average number of students in the 10 classes is same as the average of the above list.
The mean of the list 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88 = middle Two numbers/2
=> 72+74/2 = 73
Plus the number of students are more than 63
So the given possible set no. = 4
Also the mean of all number = mean of 10 class students number
The only set possible having 73 as mean ranges from 64, 66, 68, 70, 72, 74, 76, 78, 80, 82.
Sum of (x-mean)^2 = 81+49+25+9+1+1+9+25+49+81 = 330/10 = 33
SD = √33
(Sufficient)

IMO B

Posted from my mobile device