Represent Problems with an Unknown Equation

How the lesson starts: Represent Problems with an Unknown Equation

Captain Nova's stars
Hello, space cadet! Captain Nova collects star crystals. She had some, found 7 more, and now has 25. How many did she start with? We don't know yet, so we call it n!
The mystery box
Picture a mystery box. Inside are the stars Nova started with. We call that box n. Add the 7 stars she found. The total is 25. So the equation is n + 7 = 25.
Write the equation
Nova had some stars. She found 6 more and now has 20. Had some: that's n. Found 6 more: that's plus 6. Now has 20: that's equals 20. So n + 6 = 20. Watch out: found means more, so it's plus, not minus!