After a test, the marks of 24 students have been grouped in the table below : 
  | grade n | `0<=n<4` | `4<=n<8` | `8<=n<12` | `12<=n<16` | `16<=n<=20` | 
  | Number of students | 2 | 4 | 8 | ? | 5 | 
 
  1. What is the number of students having obtained a mark between 12 and 16 (excluding 16).
 2. How many students got less than 12?