To figure out what percentage, there is a simple equation:
The part is 2 billion (or the part of the original number that is left) and the whole is 7 billion. This would end up being written like:
You would then cross multiply, giving you:
2,000,000,000(100)=7,000,000,000x multiply 2 billion times 100
200,000,000,000=7,000,000,000x divide by 7 billion
x = 28.5714, or 29 % rounded up.
29% are left, to get the amount that died, just subtract 29 from 100. 100-29 = 71%
To find 1 in how many people died, first subtract 2 billion from 7 billion to figure out how many people died. This gives you 5 billion. Then take 5 billion and set it over 7 billion in a fraction and reduce.
This gives you 1 out of every 1.4 people that died. Most statistics aren't written that way, so they would probably say that either: 1 out of every 2 people died, or more accurately, 5 out of every 7 people died.
29% of the population is still living
71% of the population was killed
5 out of every 7 people died