M4.8.5 For the adult
Two equations: adding or taking away
I know x + y = 10 and x − y = 2. How do I find both numbers?
What this chapter teaches
Two unknowns need two equations. Elimination makes the coefficients of one letter equal, then adds when the signs differ and subtracts when they are the same. The other letter comes from putting the first answer back.
Three questions to ask
There is no one right wording. Listen for the idea.
- Why does one equation like x + y = 10 not give a single answer?
- When do you add the equations, and when do you subtract them?
- How can you check your two answers?
After the chapter, the learner can
- Solve two equations by getting rid of one letter
- Multiply an equation first so the numbers match
What they copy into their notebook
Match one letter, multiplying an equation if you must. Different signs: add. Same signs: subtract. Find the other letter, then check in both equations.