So, at the beginning there are a total of 25*3=75 siblings (we can assume that each of them had exactly 3 siblings, that's what average means; that we can assume this).
Now we have 25+1=26 students and the number of siblings is 75+8=83
and the average is
, and rounded it's 3.19.
Now we have 25+1=26 students and the number of siblings is 75+8=83
and the average is