Addition
WRITE FOUR RELATED FACTS FOR THE NUMBERS 8 AND 9.
8+9 = 17
9+8 = 17
17-9=8
17-8=9
What are some strategies for subtracting numbers within 20?
Counting back on a number line
Counting up on a number line
Making 10
Find a related addition fact
Which numbers are odd? How do you know?
3, 4, 7, 10, 13
3,7, and 13 are odd because they do not have a buddy.
DOUG HAS 5 ORANGES. JOE HAS 14 ORANGES. HOW MANY MORE ORANGES DOES JOE HAVE?
9 MORE ORANGES
There are 4 columns on the shelf. Each column has 3 books. How many books in all?
Draw an array and write an equation.
3+3+3+3=12
Show a making 10 strategy for 7+4
7+3=10
10+1=11
The answer is 11
Show a making 10 strategy to find 15-7
15-5=10
10-2=8
Complete the pattern of even numbers:
2, ___, 6 , 8, 10, ___, 12, ____
2, 4, 5, 8, 10, 12
Ms. Gonzalez has 12 desk pets. Then, she gets some more desk pets. Now she has 18 desk pets.
How many more desk pets did she get?
18-12= 6
12+6=18
Ms. Gonzalez got 6 more desk pets.
Mr. Ortega’s class has 9 girls and 11 boys. On the field trip students are grouped in pairs. Will everyone have a partner for the field trip?
An odd number + an odd number = an even number.
9 and 11 are both odd. When you add them together you get 20.
How does 7+7 help you solve 7+8?
7+7 = 14
7+8 is one more, so 7+8 must equal 15.
Count back on a number line to solve 17-5
17-5=12
Is 12 an even or odd number? How do you know?
Even
-Everyone has a buddy
-The ones digit, 2, is even
-12 is the sum of a doubles fact, 6+6
What strategy did you use?
8+9=17
Make a ten: 8+2=10, 10+7=17
Near doubles: 8+8=16, so 8+9=17
There are 3 tables in a classroom. 7 children sit at each table. How many children are there in all?
21 children in all.
7+7+7=21
Solve 9+9.
How did you solve it?
I know this doubles fact , 9+9 = 18
I made a ten, 9+1=10
10+8=18
Count up on a number line to show 13-8
If 8+5=13, so 13-8=5
Is the sum of 5 + 5 even or odd?
Explain how you know.
Write two more equations where the addends are the same.
It is even
A doubles fact is always even
6+6=12, 4+4=8
There are 11 boys and 8 girls in Mrs. Saso’s class. Mrs. Saso always sends students to computers in pairs. Will every child have a computer partner?
No. 11+8=19. 19 is an odd number because the ones place digit, 9, is an odd number.
Rusty places his toy trucks in 5 columns. He places 4 trucks in each column. How many trucks does Rusty have in all?
Draw a model AND write an equation.
20 trucks in all.
4+4+4+4+4=20
Write a related addition fact for 14-6
6+8=14
8+6=14
Write a related subtraction fact for 4+5=9
9-5=4
9-4=5
Second grade has 23 students.
Can they make two equal lines? Why or why not?
No. They cannot make 2 equal lines because 23 is an odd number. One person will not have a buddy.
10 students in Ms. Short’s class join 9 students at recess. Can they make 2 equal soccer teams?
No.
10+9 = 19, which is an odd number because 1 person does not get a buddy.