Relationships between Unknowns: Writing Equations

Methods in this video

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1. 1

   One amount, two ways: set them equal

   ▶ 0:46

   When to use it: The same amount is described twice, or a rule lets you build it another way (▲ × 4 = ● and ▲ + 24 = ●; the top of a pyramid is 40 and also adds up from below; several people linked by 'more' and 'times' with a total). Use one symbol for the number you don't know.

   • Give the unknown number one symbol, and write everything else with it.
   • One amount written two ways: put an equals sign between them.
   • Cross out what's the same on both sides. What's left is the difference.