Six students including A and B stand in a row. Find the probability A and B are separated by exactly one student.
Solutions · 1
Official solution
Choices for the student between A,B: 4; A,B can swap: 2 ways; treat this trio as a block along with the other 3 students: 4! arrangements.
\[P = \frac{4\times2\times4!}{6!} = \frac{4}{15}\]