+------+---------+---------+------------+
| day  | hour    | classes | projectors |
+------+---------+---------+------------+
|    1 |  9.0000 |      26 |         11 |
|    1 | 10.0000 |      30 |         11 |
|    1 | 11.0000 |      35 |         13 |
|    1 | 12.0000 |      35 |         13 |
|    1 | 14.0000 |      33 |         15 |
|    1 | 15.0000 |      37 |         15 |
|    1 | 16.0000 |      36 |         12 |
|    1 | 17.0000 |      31 |         11 |
|    1 | 19.0000 |      26 |         11 |
|    1 | 20.0000 |      29 |         10 |
|    1 | 21.0000 |      15 |          7 |
|    2 |  9.0000 |      27 |          9 |
|    2 | 10.0000 |      33 |         11 |
|    2 | 11.0000 |      31 |          8 |
|    2 | 12.0000 |      27 |          8 |
|    2 | 14.0000 |      31 |          8 |
|    2 | 15.0000 |      32 |          9 |
|    2 | 16.0000 |      27 |          9 |
|    2 | 17.0000 |      27 |         10 |
|    2 | 18.0000 |      13 |          5 |
+------+---------+---------+------------+
20 rows in set (0.04 sec)

mysql> select status, count(*) from classes group by status;
+--------+----------+
| status | count(*) |
+--------+----------+
|      0 |       14 |
|     10 |       38 |
|     30 |      291 |
+--------+----------+
3 rows in set (0.00 sec)

mysql> select count(distinct(student)) from roster;
+--------------------------+
| count(distinct(student)) |
+--------------------------+
|                     1108 |
+--------------------------+