Answer:
( About ) 1.01371e + 16 ways
Step-by-step explanation:
You have 21 choices for the first student chosen, 20 choices for the next, then 19, then 18. However, this over-counts everything by a factor of 7! (the number of ways in which four objects can be arranged with regard to order).
Thus, take a look at the procedure below;
[tex]21! / 7! =\\21 * 20 * 19 * 18 * 17 * 16 etc. / 7 * 6 * 5 * 4 * 3 * 2 * 1 =\\( About ) 1.01371e+16[/tex]
This is an approximate answer mind you, so I hope that still helps!
