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# Write an algebraic equation for the following problem and then solve it. The population of a country in 2015 was estimated to be 321.6321.6 million people. This was an increase of 22​% from the population in 1990. What was the population of the country in​ 1990?

let's say is the population in 1990 is "x". well, in 2015, 25 years later, it ballooned to 321,6321.6, and we know that's 22% or 22/100 ( 0.22 ), more than 25 years ago. if the amount on 1990 was "x", then 22% of "x" is just (22/100) * x, which is 0.22x. so, whatever "x" may be, the sum of those two is 321,6321.6, thus $\bf 321,6321.6 = x + 0.22x\implies 321,6321.6 = 1.22x\\\\\\ \cfrac{321,6321.6}{1.22}=x$