Estimation in 3rd Grade
Date: 12/16/96 at 09:50:18 From: Karen Stetchock Subject: Estimation - third grade Dr. Math, How would you suggest to teach estimation to a third grade classroom? Thanks for your help, - Karen
Date: 12/16/96 at 19:51:53 From: Doctor Tom Subject: Re: Estimation - third grade Hi Karen, I don't know how much help I'll be, since I've never been the instructor in a third grade class, but I do have a lot of experience with 7th graders, and I've tried (with less success than I'd like) to talk about estimation. I think estimation is a critical ability - I try to get students to try to estimate answers before they do any real calculation. I'd start with questions like this: Suppose you go to the grocery store and bring 5 different boxes of cookies to the cash register. The cashier rings them up, and tells you, "That'll be $452.18." How do you know he's wrong? What sorts of numbers are "reasonable"? How do you know that? Talk about how to simplify: What's 1010 times 980, approximately? Well, it's roughly 1000 times 1000, or a million. Talk about how to find "round" numbers close to the actual numbers. I made a list of questions for estimation. They're aimed at smart 7th graders, but maybe you can use some of them, or can convert them to more suitable forms for your kids. I'll append that list and some comments about it at the end. (I guess from the questions it's obvious that I live near San Francisco.) Good luck! -------- How long to drive from NYC to SF without stopping? How much does an elephant weigh? A mouse? How many tiles on the floor of this classroom? How many parts in a bicycle? How many turkeys to feed all the kids at this school for Thanksgiving dinner? In those crime movies, you see briefcases full of $100 bills. How much is such a briefcase worth? How long could you live on $1000? How many miles of roads in San Francisco? How much money (in coins) could you carry? How many feet of yarn in a sweater? How much water in a bathtub? How many leaves on an oak tree? How many kernels on an ear of corn? How much gasoline in a big tanker-trailer? How far could you drive using it? Catch 100 fish in a lake, tag them, and toss them back. Tomorrow you catch 100 more, and 10 are tagged. About how many fish are there in the lake? ________ The hardest thing about this exercise was trying to get across the idea that I didn't expect an exact answer - just a good answer. Many of the kids seemed to think that if the answer wasn't exact, then any wild guess was as good as any other. I still haven't made this work as well as I'd like, but I think the idea is critically important. Whenever I start a mathematical calculation, I do a rough calculation in my head so I know if my calculated answer is in the right ballpark. -Doctor Tom, The Math Forum Check out our web site! http://mathforum.org/dr.math/
Search the Dr. Math Library:
Ask Dr. MathTM
© 1994- The Math Forum at NCTM. All rights reserved.