3 act task: mowing the lawn

We worked on composite area and pythagorean theorem today in grade 9. There’s a good 3 act task called mowing the lawn. It starts with a lawnmowing video to pique the interest, and get questions flowing.

Next, another video, with a timer, and also dimensions given for the mower and for the lawn

I usually wait until they ask how wide the mower is. Often we get so bogged down with area calculations that we forget the mower has a width too!

We then worked really hard for quite a while to calculate the area of the lawn and how long it would take to cut.

Some common errors I’ve noticed were in applying pythagorean theorem to calculate a triangle leg vs hypotenuse. Also some students struggled with 18 inches being 1 foot 6 inches which is 1.5 feet (not 1.6 feet). Others struggled with how to use unit rates that would be helpful like how many seconds it takes to cut one square foot of lawn. That can then be scaled up to figure out the time to cut the entire area of the lawn. There were good conversations about how many pieces to break the yard up into, and if it mattered if he mowed in a spiral pattern or back and forth in rows.

I’m thankful that our meter sticks are also yard sticks, so we can work in inches and feet when we need to.

In the end we watched the whole video to see the answer. Watch for motion sickness!

We did a lot of calculating and reasoning today. We need to work on our communicating…that will be our next step.