Susan solved 200-91 and decided o add her answer to 91 to check her work. Explain why this strategy works

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(1) Answers

FloriaDemus573

Think of an equation:
200 - 91 = 109
You can do anything to this equation, as long as you do the same thing to both sides. So, if you add 91 to both sides, you will get:
200 = 200
Since this holds true, Susan's strategy to add her answer to 91 makes sense.