Math

Unit 3- Mental Math

BIG IDEA: I can add and subtract using different mental math strategies when solving problems.

1. I can apply mental math strategies and number properties for basic addition and related subtraction facts to 18.

2. I can describe and apply mental math strategies for adding two 2-digit numerals.

3. I can describe and apply mental math strategies for subtracting two 2-digit numerals.

4. I can apply estimation strategies to predict sums and differences of two 2-digit numerals in a problem solving context.

2 Digit Subtraction Strategies:

1. Use addition for subtracting

45- 30=

Think: 30 + _____= 45 (30 + 10 =40 40 + 5 = 45 so 10 + 5 = 15) Some students will know that there are 15 steps between 30 and 45)

2. Use a number line and put the smaller number on the left and the larger on the right. Jump to the friendly #s and count the number of steps between them.

_*___________________________*_______________*__________________________________________________

30 (+10) 40 (+5) 45

3. Subtract the rods (tens) first, then subtract the singles (ones) (Subtract from LEFT to RIGHT)

45 - 36=

45 - 30= 15

15 - 6 = 9

Examples of Mental Math Strategies

Strategy	Example	Description
Counting On--adding 1,2, or 3	8+2=	Start at 8, count on 9, 10
Counting Back	8-2=	Start at 8, count back 7, 6
Doubles	6+6=	Double all the numbers 1 - 9 We also need to know larger doubles. (10 +10, 15+ 15, 25 + 25...)
Near Doubles (1)	7 + 8=,	Doubles+One More I know that 7 + 7= 14 so 7 +8= 14 +1 + 15 Double - One More I know 8 +8 = 16 so 7 + 8 = 16-1 = 15
Near Doubles (2)	7+9=	Doubles + Two (7+7+2) or Doubles -Two (9+9-2)
Making Friendly Numbers	8 +5	8+2=10+3=13

We spent a whole day doing math. (The students voted on this!) We played a lot of math games and here is a fun and challenging game. Arrange the numbers so all the lines equal the same amount!http://www.oswego.org/ocsd-web/games/Powerlines/powerlines1.html

If you completed the first phase, use the password to continue on to the 2nd;

http://www.oswego.org/ocsd-web/games/Powerlines/powerlines2.html

and here is the 3rd:

http://www.oswego.org/ocsd-web/games/Powerlines/powerlines3.html

Here is a link to a money game. Copy & paste it to your browser.

http://exchange.smarttech.com/details.html?id=x0036f44cc8e5472e9c69797349b4f0bd

Another fun math link:

http://www.mathsisfun.com/index.htm

http://www.mathplayground.com

We have started our 2nd unit in Math-- Numbers to 1000 . Listed below are the outcomes we will be working on.

BIG IDEA- I can use what I know about number to solve problems efficiently.

I can skip count forward and backward by 5, 10 and 100s using any starting point.
I can skip count forward and backward by 3, 4, and 25s using multiples of 3, 4, and 25 as starting points.
I can show and describe numbers to 1000 by using objects, drawings, and symbols.
I can compare and order numbers to 1000.
I can use referents to estimate quantities less than 1000.
I can show the meaning of place value for numbers up to 1000 by using object and drawings.

IMPORTANT WORDS

ascending order, descending order, digit, estimate, expanded from, number expression, place value, referent, standard form, skip counting

We have finished our first math unit, Patterns and Relations. The big idea was:

I can use increasing and decreasing patterns to describe the world and the solve problems.

The students are describing, extending comparing, and creating patterns using objects, drawings, sounds and actions.

Here is a site that has math games for grade 3

Here is a link to 2 websites that have a lot of math activities as well as activities for all the subjects.

http://blogs.gssd.ca/mmorley

http://www.blackgold.ab.ca/ict

I am focusing a lot on problem solving this year. We do a word problem every day. There are many ways to solve problems so I am encouraging the students to try to solve each problem on their own first. The most important thing is to get the students thinking about what the problem is asking instead of ME telling them what to do. This can be frustrating for them in the beginning but they will begin to be more independent. It is fun to see the different ways students solve problems. We often share our strategies with each other once everyone has tried the problem.