The data below are students' marks on a class test where the maximum mark was 30. They have been sorted into ascending order.

6
8
10
11
11
11
12
12
12
12
12
14
14
14
15
15
15
16
16
16
16
17
17
17
17
17
17
18
18
18
18
18
19
19
19
19
20
20
20
20
20
21
21
21
21
21
22
22
22
23
23
23
23
23
23
23
23
23
23
24
24
24
24
24
24
24
24
24
24
25
25
25
25
25
26
26
27
27
27
27
27
28
28
28