The correct options are
A Total number of people in 0-20 age group is 10
C Maximum number of people are from age group of 21-30 years
The number of people in a class is proportional to area.
Therefore, the class of 0-20 is twice the size of other classes.
So, total frequency of 0-20 class is 5x2=10
Hence option A is correct and B is incorrect.
The class of 21-30 age group has the highest frequency.
Hence option C is correct.
On summing up all the frequencies, it can be seen that D is incorrect