Wednesday, October 28, 2009

Literal Equations

We've moved on to solving literal equations for a variable. I like this transition because it reinforces the same skills they've been working on forEVER. One thing came up in my first of 3 classes to teach it this year that made me change tactics for the next 2 classes.

We were all about "isolating the variable" and "undoing what's done to the variable you're solving for" and such. Then as I'm walking around, lo and behold, a student was actually moving the variable. She wanted to get it to the other side. What was she doing?! Don't touch that variable!

That led to the following in my next 2 classes. Suppose the problem is
Solve 3A = 2w + 4p for w.
I first made them get out another colored pen/pencil, and then identify the variable they were solving for. Then they had to write that variable in a DIFFERENT color:

3A = 2w + 4p

Then I made them draw an arrow to the w and write in their notes, "DON'T TOUCH THIS" while humming the M.C. Hammer song of the same name. We continued on, and most everyone successfully colored the "solve for" variables and left them alone in the remaining problems.


  1. Er...*always* don't touch this?

    qr = (1 / x)

    q != 0, r != 0

    Solve for x.

    Sure, you could write the right side as x^(-1) and then raise both sides to the -1, but I think your students would still consider that touching the variable.

  2. Anonymous12:06 PM

    Ah! Good point ... I need to in the future amend that to "only if it's on one side and in the numerator".... Future bridge for problems like:
    2x + 5y = 7x + 3 and solve for x.

    Ms. Cookie