The past few days we've been solving equations and they're doing great. Today I started class by giving them this worksheet:
When I handed it out I said two things:
- These scales are all currently balanced. You must choose a number to fill into the boxes in each problem that will keep them balanced.
- Whatever number you choose for a problem, you may ONLY use that number.
At one point a boy asked if they could use negatives. I referred back to the two rules, as long as it is a number they could try it. The other kids heard this and decided that MUST be the trick. It has to be a negative number. No luck. The same thing happened when using 0 and decimals were suggested.
After letting them suffer for a little bit [note: they never stopped trying, not a single one of them gave up..they all wanted badly to be the one that figured it out] we went over them. I went around the room and had every kid call out their answer to each one, writing the answers down as we went along. Also I saved #3 and #6 for last which killed them.
For #1 & #4 everyone got different numbers and we discussed if that was ok. They decided it was ok. I asked which one of the numbers was the "correct" one and they agreed that they were all correct possibilities.
For #2 & #5 everyone got the same answer and we discussed whether there were any other possible answers. They said there was not.
On to #3. They were so excited. Everyone got real quiet. They couldn't wait to hear the answer. I started by covering up the numbers 20 and the 13.
Made sure that we were all on the same page and agreed that at this point every single number would work (like in #1). Then I asked what would happen to a balanced scale if we put 20 onto one side and 13 onto the other side. They said it wouldn't be balanced anymore.
I revealed my secret to them that there was in fact no possible answer. Discussed that the real problem was when I lied and told them that all the scales were balanced. Then they went crazy saying they KNEW it wasn't going to work!! They were thrilled that they were right.
Afterwards we made the following foldable for their notebooks:
I love lessons that go like this. It is so rewarding and fun when they get so into an activity. These are the times when I feel like they are really learning. They will remember their frustration over the no solution scales and they really developed an understanding of exactly why equations like this do not have an answer. They also have a much stronger understanding of why identities have infinite solutions. I feel now that when they give these as answers to equations they know why they are writing those words down.