The  table shows the distribution of ages of 22 students in a school.
                        
                        
                          
                            | Age (years) | 12 - 14 | 15 - 17 | 18 - 20 | 21 - 23 | 24 – 26 | 
                          
                            | Frequency | 6 | 10 | 3 | 2 | 1 | 
                        
                        Using an assumed mean  of 19, calculate, correct to three significant figures, the:
                        
                          - mean  age;
- standard  deviation;
 of  the distribution.