For a frequency distribution with classes 0-10, 10-20, 20-30, the class mark of the second class is: MCQ with Answer and Explanation

Explanation:
CDR uses total population, so countries with older populations (e.g., Japan) have higher CDRs even with better age-specific survival than younger populations (e.g., Nigeria), necessitating age-standardization.

Explanation:
Mean changes by the same amount as the change in origin.

Explanation:
The median can be determined even if the extremes are open-ended, as long as the median class is closed.