You can
put this solution on YOUR website!P(student in a particular group) = 1/3
So, P(all 3 in first group) = (1/3)*(1/3)*(1/3) = 1/27
Also, P(all 3 in second group) = 1/27 too
and P(all 3 in third group) = 1/27 also
So, P(3 friends are all together) = 1/27 + 1/27 + 1/27
P(3 friends are all together) = 3/27
P(3 friends are all together) = 1/9
jon.