when they round. Students should have numerous experiences using a number line and a hundreds chart as tools to support their work with rounding. Example: Your class is collecting bottled water for a service project. The goal is to collect 300 bottles of water. On the first day, Max brings in 3 packs with 6 bottles in each container. Sarah wheels in 6 packs with 6 bottles in each container. About how many bottles of water still need to be collected? Student 1 First, I multiplied 3 and 6 which equals 18. Then I multiplied 6 and 6 which is 36. I know 18 plus 36 is about 50. I’m trying to get to 300. 50 plus another 50 is 100. Then I need 2 more hundreds. So, we still need about 250 bottles. Student 2 First, I multiplied 3 and 6 which equals 18. Then I multiplied 6 and 6 which is 36. I know 18 is about 20 and 36 is about 40. 40 + 20 = 60. 300 – 60 = 240, so we need about 240 more bottles. Example: On a vacation, your family travels 267 miles on the first day, 194 miles on the second day and 34 miles on the third day. How many total miles did your family travel? Some typical estimation strategies for this problem are: Student 1 I first thought about 276 and 34. I noticed that their sum is about 300. Then I knew that 194 is close to 200. When I put 300 and 200 together, I get about 500. Student 2 I first thought about 194. It is really close to 200. I also have 2 hundreds in 267. That gives me a total of 4 hundreds. Then I have 67 in 267 and the 34. When I put 67 and 34 together that is really close to 100. When I add that hundred to the 4 hundreds that I already had, I end up with about 500. Student 3 I rounded 267 to 300. I rounded 194 to 200. I rounded 34 to 30. When I added 300, 200, and 30, I know my answer will be about 530.
Similar to other procedures in your classroom, there are several elements that must be in place to ensure students get the most from their Number Talk experiences. These elements are: A safe environment Problems of various levels of difficulty that can be solved in a variety of ways Concrete models Opportunities to think first and then check Interaction Self-correction For further details on implementing Number Talks, see: Estimation 180 Estimation is a skill that has many applications, such as checking computation answers quickly. Engaging in regular estimation activities will develop students’ reasoning skills, number sense, and increase their repertoire of flexible and efficient strategies. As students gain more experiences with estimation, their accuracy will improve. According to John Van de Walle, there are three types of estimation that students should practice: Measurement estimation – determining an approximate measurement, such as weight, length, or capacity Quantity estimation – approximating the number of items in a collection Computational estimation – determining a number that is an approximation of a computation One resource which provides contexts for all three types of estimation is Andrew Stadel’s website, . In his website, Mr. Stadel has posted daily estimation contexts. Here are his directions for using his website: Click on a picture. Read the question. Look for context clues. Make an estimate. Tell us how confident you are. Share your reasoning (what context clues did you use?). See the answer.