Class #21--5th Grade Math

Tuesday, November 9, 10:15 A.M. 5th Grade Math Class. Class #21 on my “50 Classes or Bust!” journey. As I walk into room 314, Mr. Rossi is reviewing the schedule for the next few days of class. He then asks a student to uncover the first objective for the day by using the “eraser” mode on the SmartBoard: to round any decimal up or down to deal with estimates in real situations. Mr. Rossi is an avid user of technology in his math classes. Whenever I walk by his room, he is using the SmartBoard, which the students really enjoy. The class briefly reviews decimal estimation with multiplying and dividing. The key word to remember when estimating, a boy mentions and Mr. Ross affirms, is “about.” An estimate needs to be “about” the exact answer, but one can save time by not finding the exact answer. Estimation is a very important tool in the math toolbox. Another student uncovers the second objective for the day, which is hidden in a different corner : to use metric units of mass and capacity. Here is a question to shake the metric rust off my readers’ brains: when converting from meters to kilometers, do you divide or multiple? The answer is…divide. Although it seems counterintuitive, when you convert from a smaller unit to a bigger unit, you divide, because you end up with fewer of the bigger units, e.g. 2,000 meters = 2 kilometers. Throughout class, Mr. Rossi has the students working in three groups of four. They are tasked with figuring out questions to ask the other groups related to the topics being discussed at the moment. For example, “Tom and four friends each won lottery jackpot of $2.541M in a lottery. About how much was the total jackpot?” After rounding 2.54 to 3, the class decided that $15M was the estimation. The class then had a discussion of whether to round a number like 247 to 200 or to 250 when rounding, as in “About how much is 247 x 2?” Mr. Rossi explained that estimating should, ideally, be done in your head, so either 200 x 2 or 250 x 2 is appropriate, given what each student can do in his/her head. He stressed that the purpose of estimation is to find an approximate, not an exact, answer. Bravo to Mr. Rossi and his students for an enthusiastic, chock-full math class!