Correct Answer - a
The sum of the weight of the 9 students = `25 xx 9 = 225` kg .
If one more student is joined in the group , then total number of students is 10 , and the mean is 25 .
The sum of the weights of the 10 students is `25 xx 10 = 250` kg .
The weight of the 10th student is `250 - 225 = 25`kg .