Bring in a large cylindrical glass jar that is filled with marbles of different shapes and sizes.

Also bring in a tiny cylindrical glass jar that is filled with marbles.

Tell the students the amount of marbles that are in the tiny jar.

Their task is to estimate the number of marbles in the large glass jar.

Divide the class into teams and have them work at the problem together.

They can use paper to write down ideas for how they would come up with their estimates but not for any calculations. They must do those with mental math!

For example, they could estimate that the large jar would hold 30 of the small jar so if the small jar contains 23 marbles, the large jar would contain 30 x 20 roughly or 600 marbles.

Once they have all come up with their mental math answers and recorded them it’s time to tackle the problem by comparing the volumes of both cylinders and getting a closer calculation. Have students measure the height and radius for each jar and compute the volumes and compare them to make their more precise estimates.

At the end of the activity, have students count the marbles in the large glass jar and compare them to the mental math answers they came up with.

You can also download the PDF version of this game to file away for later HERE