Saturday, April 3, 2010

MAM Day 3: Estimation

Yesterday we talked about counting, which is getting an accurate number. Today I'll briefly talk about estimation, how, when, and where we use it.

My first thought was estimating how many jellybeans are in the jar. Thanks to Wendy, who is the Math Rules! Manager at Boston Partners in Education, we have Easter candy to munch on. Chocolate isn't my favorite, but the jars full of jelly beans are awesome. We've all done it at some point in school or seen it at a fair - guess how much is in the jar. While I don't have any advice for getting the right answer, winning the prize depends on how well you can estimate.

Estimation is using a logical reasoning process to guess at an answer - how many jelly beans, or how much time it will take, or how many people are in the auditorium, or approximately how much food we'll need for an event.

I've used estimation for large scale shopping. My sisters and I used to go thrift shopping on big 50% off sale days and we would have to estimate approximately how much money we spent. I also use estimation when I go grocery shopping. My siblings and I used to play a game where we would 'The Price is Right style' guess the closest total cost without going over. It's a fun estimation game that my family of nerds liked to play. I would suggest you try it out sometime with your friends, family, roommates, and anyone else.

Estimation can also be used in grade school math. Working with elementary students, we haven't gotten to a point where my students use estimation to help them check their answers. We're still very focused on getting the one right answer to the question. I would argue that students need to learn and really understand estimation before we move on to multiplication or division accuracy.

How else are students going to know if they made a mistake on a multi-digit multiplication problem? To multiply 83 x 6, a student could estimate 80 x 6 = 480 and know that their answer should be a little more than 480. It gets harder with more digits. 314 x 57 can be rounded off and estimated at 300 x 60 = 18000. It would help if a student forgot a place value zero, or multiplied wrong to check their answer. If they got an answer in the low thousands, they could realize and start over.

Estimation only works if you're using logic to make an educated guess. Sure, I can estimate there's one million jelly beans in the jar, but it doesn't make sense and I wouldn't have won the prize. Estimation works well within valid reasoning of your guess. I could guess there are three jellybeans in the jar, but that's also a bad estimation.

So I took this jar and asked some of my co-workers how many they thought were in the jar. My supervisor Erin was the closest. Post any guesses or strategies for these types of games! If you feel compelled to share an example of estimation, I will give you a handful of jellybeans as a prize!



  1. Though I'm delighted to be currently in the lead, I think I've got an advantage since the picture of the jar seems to be MIA! :)

  2. My bad! I forgot to download the picture off my camera :)

  3. Untrue, my friend. I am just an outrageously good estimator! Could you simply be...jealous?