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Grade 6 Math · Level 6, Grade 7 Preview

Add & Subtract Rational Numbers

How the lesson starts: Add & Subtract Rational Numbers

1. Mo's burrow elevator

   Hi there! Mo the mole lives in a giant burrow tower. The ground floor is 0. Floors above are positive. Floors below are negative. Mo starts on floor −3 and rides up 5. Where will he end up? Let's find out!

2. Adding moves right

   Turn the elevator on its side and you get a number line. Here is Mo at −3. Here is where he lands: 2. Why? Adding 5 means 5 steps right. 3 steps reach 0, then 2 more. So −3 + 5 = 2.

3. Subtracting moves left

   Now Mo rides down. Subtracting moves left. Here is Mo on floor −5. Here is where he lands: −8. He rode down 3, so 3 steps left. −5 − 3 = −8. Going down from a negative floor goes even deeper.