In our math class we have begun learning about subtraction. The first strategy we are practicing is called “subtract the ones last”
Example 1:
68 – 15
Start at 68 and subtract 10, then 5.
68 – 10 = 58
58 – 5 = 53
So, 68 – 15 = 53
This strategy also works when subtracting numbers with 3-digits.
Example 2:
568 – 474
Start at 568 and subtract 400, then 70, then 4
568 – 400 = 168
168 – 70 = 98
98 – 4 = 94
So, 568 – 474 = 94
Tuesday, February 8 – Learning Conferences
Thursday, February 10 – Learning Conferences
Friday, February 11 – Dress up for Olympics
Monday, February 14 – Valentine’s Day
Wednesday, February 16 – Wear Pink
Monday, February 21 – Winter Break begins
Monday, February 28 – Classes Resume
Monday, March 7 – No classes for students
We will be exchanging Valentine’s Day cards in our classroom. Please be sure to send cards only (no treats.) This is just to keep up with all safety protocols as well as comfort level for everyone. Please help your child complete their cards and bring them to school no later than Thursday, February 10th. We will quarantine the cards before exchanging them on February 14th. Your child will be bringing home a list of names this week to help them make their cards and be sure not to leave anyone out. If you have any questions or concerns about this please let me know.
Click the link below for instructions:
Two and Three Digit Addition:
We continue to work hard at maximizing our learning about numeracy while exploring addition and subtraction of two and three digit numbers. The students have many strategies for working with three digit number equations. The samples below are examples of some of the strategies we have been working with. Please keep in mind that these are just basic examples and individual students will often take apart and re-construct the numerals in unique ways that match their understanding of numbers. When this happens it is often a very good sign that they are good mathematical thinkers. There is a big difference between blindly following steps to get the correct sum and being able to make efficient adjustments to strategies based on the problem that is presented.
Addition:
368+257=
300 + 200 = 500 (add the hundreds)
60 + 50 = 110 (add the tens)
8+7 = 15 (add the ones)
500 + 110 = 610 (add your answers from the 100s, and 10s)
610 + 15 = 625 (add answer from the 1s the sum of the 100s and 10s)
Another Variation
368
+ 257
_15 (add the ones)
110 (add the tens)
500 (add the hundreds)
625
For both addition and subtraction some students need to build/draw base 10 materials to help them visualize what is happening to solve three digit problems.
The students bring rich math strategies with them to grade three. Most of the strategies we generate come from the student’s ways of thinking about numbers. This is good because it often helps them see that they already have good ways of working with numbers. Some of our best thinkers don’t believe they are good at math. Helping kids use and refine their own strategies is the best way we can help them become more confident and value their own thinking.
Estimating Sums: We use the following three strategies to help us build mental math skills. We focus on learning the strategies and practice deciding which strategies gives the best estimate based on the numbers presented in the problem. I can understand that some people may have a glance at the examples below and feel that it seems a bit silly to estimate. I can reassure you that it is worth the short time we spend on it. Many of the mental math strategies people use resemble some of these estimation strategies. For students who are having a tougher time breaking apart numbers and reconstruct them in their mind, estimation is a good first step. It helps them find an easy way to “get close” to the sum or difference and learn to clean up the left over bits later. Students who already have favorite mental math strategies often discover new ones as we discuss estimation. Once they have a few strategies to work with, they can begin learning to choose the most efficient strategies to use depending on the numbers presented in the problem. In short, we have very rich conversations and great thinking springs from our simple estimation strategies.
1. Take both numbers to the closest 10.
59+23
60+20=80
So, 59+23 is estimated to be 80.
2. Take one number to the closest 10.
59+23
60+23=83
So, 59+23 is estimated to be 83
3. Add only the digits in the tens place.
59+23
50+20=70
So, 59+23 is estimated to be 70.
Here is a quick overview of what we have been practicing so far in our Addition and Subtraction unit. We are working with 2 and three digit numbers now, but these are some of the important single digit strategies that we have reviewed. I will post more about some of the other strategies we have been working with soon!
1. Doubles and Near-Doubles Addition Facts: We spent quite a bit of time practicing our doubles facts as a class and individually. We focus on doubles because they are often easy to learn and can be a helpful mental math strategy for solving other addition facts that are close to the double. Students practiced solving “near doubles” equations and explaining the strategy as clearly as they can.
Example:
6+8=?
I know 6+6=12
6+8 is 2 more.
So, 6+8=14
or
I know 8+8=16
6+8 is 2 less.
So, 6+8=14
2. Making 10:
Example: To solve 6+8 we may think: Take 2 from the 6, leaving 4. Add 2 to the 8 to make 10, then add the 4 to get 14.
Or, use an adding a 10 fact like the example below.
We know 10+6=16.
8+6 is 2 less.
So, 8+6=14.
We have also been practicing our addition facts that make 10.
3. Related Addition and Subtraction Facts (Fact Families):
Example: If we know 7+6=13 we also know 6+7=13, 13-6=7, 13-7=6. Using “fact family” knowledge is often most useful for students to solve subtraction equations by thinking of the related addition fact.
Friday, January 14– SRC Spirit Day: Dress up like a teacher
Friday, January 28 – SRC Spirit Day: Anything But a Backpack
Monday, January 31– No school -PD Day
February 8th and 10th– Learning conferences (3:00-7:00)
Your child’s class is starting a mathematics unit on addition and subtraction. Your child will develop strategies for adding and subtracting whole numbers by using addition charts, mental math, estimation, Base Ten Blocks, place-value mats, and pencil and paper.
In this unit, your child will:
The ability to use a variety of strategies to add and subtract leads to the development of a strong sense of number.
Here are some suggestions for activities you can do with your child.
The students worked very hard on their Grinch portraits. They are very proud of their masterpieces and would like to share them with you!
