What is the relationship between air density and air pressure and air temperature? (simple explanation needed)?

Some textbooks and online sites are stating as air pressure decreases so does air density (proportional) and so does temperature.. but then others are stating the opposite, that as air pressure and temperature decreases, the air density increases. I just want a simple explanation without going deep on the various... show more Some textbooks and online sites are stating as air pressure decreases so does air density (proportional) and so does temperature.. but then others are stating the opposite, that as air pressure and temperature decreases, the air density increases. I just want a simple explanation without going deep on the various formulas and theories. Which is correct?
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