The table shows information about the age, a a\,a years, of 40 members of a local chess club.
| Age (a a\,a years) | Frequency |
|---|---|
| 10<a≤2010 < a \leq 2010<a≤20 | 8 |
| 20<a≤3020 < a \leq 3020<a≤30 | 15 |
| 30<a≤4030 < a \leq 4030<a≤40 | 11 |
| 40<a≤6040 < a \leq 6040<a≤60 | 6 |
Find the class interval that contains the median age.
Work out an estimate for the mean age of the members.