I used three sizes of marshmallows – small, large, and those crazy jumbo-sized ones. The little marshmallows had a value of one, the large ones had a value of ten, and the big honkin’ ones were worth 100. I explained this to my son and gave him an answer sheet with this key at the top.
I started by giving him just three little marshmallows and asking him to add them up. Simple. Then I added some large-sized marshmallows. Lastly I added some of the biggest marshmallows. At first my son was adding them (i.e. 100, 200 … 210, 220 … 221, 223, 224). I gave my son a 1-100 numbers grid to use in case he needed it; he didn't (yahoo!).
Then I explained that when you have a number in the hundreds, the number will have three digits. I made three lines on his answer sheet and asked him how many jumbo marshmallows were on the table. “Two,” he said. I told him to write it on the first line. Next I asked how many large marshmallows were there. “Two.” He added this to the second line. Finally, I asked how many little marshmallows (i.e. ones) there were. “Four.” Now he had the answer: 224.
We ran through a number of problems, with answers that ranged from 22 to 955. To wrap up our activity, I put three jumbo marshmallows and two little ones in front of him. I could see him thinking this through before he added three lines and wrote 302. “That’s right! There are no tens so you write a zero in that spot. Great job!”
To reward him for all that hard work, I whipped up some rice krispie treats. What else am I gonna do with all those marshmallows? MMMMmmm. (I’m really starting to like these math activities!)
Want to download the Marshmallow Math answer sheet? A free download is available here.