Unit 5: Addition & Subtraction to 100

Here are some of the strategies that may be new for your parents. We will use these ones, along with some of the more traditional strategies.

Addition Strategies:

Front End Addition - 
"I can use front end addition when I add numbers with two digits."

Example 1:
34 + 25

30 and 20 makes 50. 4 and 5 makes 9.
50+9 =59

Example 2:
34 + 27

30 and 20 makes 50. 4 and 7 makes 11.
50+ 11 --> 50 + 10 + 1 = 61

Subtraction Strategies:

Compensation - 
"I can use compensation when I see a subtrahend that is an 8 or a 9 (or has an 8 or a 9 in the ones place)."

Example 1:
27-8

First, I will think 27-10 = 17. Now because I subtracted " 2"  too many from the original equation, I will add " 2 " to the answer to make 19.

Example 2:
56-19

First, I will think 56-20 = 36. Now because I subtracted " 1 " too many from the original equation, I will add " 1 " to the answer to make 37.

Expanding the Subtrahend - 
"I can expand the subtrahend when I solve a two-digit subtraction equation."

Example 1: 
54-13

First, I can do 54-10 and then subtract 3 more.

Example 2:
45-27

First I can do 54-20 and then subtract 7 more.

Important Vocabulary:

Addend = a number that is added to another
Subtrahend = the number that is to be subtracted
Minuend = the quantity from which the minuend is to be subtracted
Sum = the answer in an addition equation
Difference = the answer in a subtraction equation
Equation = a statement that says two things are equal