Solve 2 math problems and show detailed explanations

1. Of the global population that was born in the year 1920, what percentage of them passed away in the same exact time zone as they were born in? Please provide your thought process. 

2. The following statement is true: A square has four sides. However, the converse would be false as not all four-sided polygons are squares. Please provide another example. Bonus if you provide it in formal mathematical notation.