Answer: If in 1980 we had N people who were at least 100 years old, then in 2010 we had N*1.66 people who were at least 100 years old.
Explanation:
A really simple conditional statement can be written as:
If P, then Q
Where P is the hypothesis, and Q is the conclusion.
In this case, we know that:
"The number of people with age equal or larger than 100 years old, grew about 66% from 1980 to 2010"
This means that if in 1980 we had N people in that age range, in 2010 we have N*(166%/100%) = N*1.66
Then we can write a conditional statement:
If in 1980 we had N people who were at least 100 years old, then in 2010 we had N*1.66 people who were at least 100 years old.