Editing Subtraction (section)

==Units of measurement==
When subtracting two numbers with units of measurement such as [[kilogram]]s or [[pound (mass)|pound]]s, they must have the same unit. In most cases, the difference will have the same unit as the original numbers.

===Percentages===
Changes in [[percentage]]s can be reported in at least two forms, [[percentage change]] and [[percentage point]] change. Percentage change represents the [[relative change]] between the two quantities as a percentage, while [[percentage point]] change is simply the number obtained by subtracting the two percentages.<ref>Paul E. Peterson, Michael Henderson, Martin R. West (2014) ''Teachers Versus the Public: What Americans Think about Schools and How to Fix Them'' Brookings Institution Press, p. 163</ref><ref>Janet Kolodzy (2006) ''Convergence Journalism: Writing and Reporting across the News Media'' Rowman & Littlefield Publishers, p. 180</ref><ref>David Gillborn (2008) ''Racism and Education: Coincidence Or Conspiracy?'' Routledge p. 46</ref>

As an example, suppose that 30% of widgets made in a factory are defective. Six months later, 20% of widgets are defective. The percentage change is {{sfrac|20% − 30%|30%}} = −{{sfrac|1|3}} = {{sfrac|−33|1|3}}%, while the percentage point change is −10 percentage points.