Math Help - number of combinations

1. number of combinations

in how many ways can 7 out of 21 students catch the flu

2. Combinations.
${21 \choose 7} = \frac {21!} {(7!)(14!)}$

3. Originally Posted by aymers14
in how many ways can 7 out of 21 students catch the flu
Only 1 way....when each of the 7 come into contact with the flu virus.