Determine a number of years for length of reign such that half of these 40 rulers reigned more years than that number and half reigned less years than that number.

Darius is 4 years older than Shannon. In 9 years the sum of their ages will be 88. How old is Darius now? years old ● Question 17

. The earth has more than 7 billion people and almost no one lives 100 years. Assume that nobody make it past age 100. How do you know that, some year soon, more than 50 million people will die