Curriculum › Math ›Grade 6

Grade 6 Math · Level 3, Expressions, Equations & Inequalities

Test Solutions by Substitution

How the lesson starts: Test Solutions by Substitution

1. Castle of locked doors

   Welcome to Juno's castle! Every door has a number lock with an equation on it. This door says x + 5 = 12. Juno holds a ring of keys: 5, 7 and 9. Which key opens the door? Let's learn to test keys by substituting!

2. Try each key

   To test a key, swap it in for x and check both sides. Key 5: 5 + 5 = 10. Not 12, no. Key 7: 7 + 5 = 12. Yes! Key 9: 9 + 5 = 14, no. A number that makes the equation true is called a solution. Only 7 works.

3. The garden gate

   The garden gate has a different lock: n < 8. The sign means is less than. Test key 5. Swap it in: 5 < 8. Is 5 less than 8? Yes! The statement is true, so 5 opens the gate. Swap in, then ask if it's true.