Solving Systems with Elimination

Today grade 10s are starting a new cycle of learning. We started off thinking classroom style at the boards to do a three act task.

We noticed that they are weighing piles of tech devices.
we watched 3 parts of Act 2 and wrote down information and equations, and started to solve for the weight of each device.

It was a hive of activity as students attempted for the first time to solve a system of 3 equations with 3 variables.

Students noticed that by subtracting 2 equations they could determine one of the values, and they then could use substitution and the 2 remaining equations to solve.

It was interesting to see how students drew out their first steps and distilled the information into equations.

We talked about how to introduce variables, and how it’s best to have one letter or symbol represent one variable, and how choosing letters that do not look like numbers or symbols are better choices. In the following example the choice of “o” as a variable is challenging as it looks like 0.

There were high fives today as students figured out how to solve problems with the new method of elimination.

Here are the problems we worked through. We could use substitution to solve these, but since we have equations with coefficients for each variable it is an easier process to use elimination.