Question

In how many ways can a teacher divide a class of 21 students into groups of 7 students each?

Answer 1

\[ \binom{21}{7} \times \binom{14}{7} \]

Answer 2

no i dont think so the answer is suppose 66 512 160

Answer 3

\[\frac{21!}{7! \cdot 7! \cdot 7! \cdot 3!}\]

Answer 4

looks like i forgot to remove are arrangements.
\[ \frac{\binom{21}{7} \times \binom{14}{7} }{3!} \]