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Grade 3 Math · World 2: Add-and-Subtract Express · Level 19
A Letter for the Unknown
Write and solve equations like n + 245 = 600.
Warm-up, learn, try it together, practice, then a quick check. About 15 minutes.
What children learn in Level 19
- A letter can stand for a number we don't know yet. In n + 245 = 600, n is the missing part.
- To find n, think: 245 plus what makes 600? Or subtract: 600 minus 245 is 355. So n = 355.
- Check by putting it back: 355 + 245 = 600. It works! That's how you justify your answer.
Georgia's K-12 Mathematics Standards:
- 3.PAR.2.2 — Apply part-whole strategies, properties of operations and place value understanding, to solve problems involving addition and subtraction within 10,000. Represent these problems using equations with a letter standing for the unknown quantity. Justify solutions.