Unit A: Addition, Subtraction & The Number System within 100
What Your Child will Learn in Grade 2
- Use a variety of strategies for adding and subtracting within 100
- Use addition and subtraction within 100 to solve word problem
- Add up a collection of coins total up to 25¢
- Represent mathematical situations with pictures, numbers, equations, and words
Vocabulary
Addend-any number being added.
Difference-the result when one number is subtracted from another.
Equation-a number sentence with an equal sign. The amount on one side of the equal sign has the same
value as the amount on the other side (Example: 6 + 4 = 10)
Expression-a mathematical phrase without an equal sign (Example: 6 + 4)
Partition/Decompose-to separate a number into two or more parts
Place Value-the value a digit has because of its place in a number.
Related Facts-Addition and subtraction facts that share the same numbers. (also known as fact family)
Sum-the answer to an addition problem.
Strategies
Adding Up-can be used to solve subtraction
48 - 22 = ? can be thought of as 22 + ? = 48
Compensation-Students remove a specific amount from one addend and give that exact amount to the other addend to make friendlier numbers.
Example: 18 + 23 = __
18 + 2 = 20
23 - 2 = 21
20 + 21 = 41
Making a Friendly Number/Using Landmark Numbers-Students adjust one or all addends by adding or subtracting amounts to make a friendly number.
Example: 23 + 48 = __
48 + 2 = 50
50 + 23 = 73
73 - 2 = 71
Partitioning-to solve 12 + 10, Leigh did the following: She partitioned 12 into a ten and 2 and used a number line to add up
-to solve 35 + 42 =
Holly recorded like this:
35 + 42 = ?
30 + 40 = 70
5 + 2 = 7
70 + 7 = 77
Activities At Home
- Coins-At home, your child can examine coins and talk with someone about what they notice. You might also help your child count the change in your pocket or change purse. Ask questions such as, “What is this coin called?” and “Can you find a quarter? How many pennies it is worth?”
- Calculator Exploration If you have a calculator at home, pose problems for one another. See which types of problems are easier to do mentally and which ones are faster with the calculator. “Is it easier to add 5 + 6 + 5 + 1 in your head or on the calculator?”
- Making 25 Cents Discuss how much 25 cents is worth in pennies, nickels, dimes, and quarters. Talk about equivalencies: “Here are 1 quarter. How much is this worth? Can you find another way to make 25 cents?” “I have 2 dimes. How much more do I need to have 25 cents?”