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Work clockwise around the circle by adding and subtracting the numbers shown to fill in the blank boxes. The last addition should result in the starting number. The first one is done for you.  
11
2
9
+6
15
4

14
+4
18
12
6
+8

17
4
13
7
6
+11

16
9
7
7
0
+16

20
15
5
+7
12
+8

5
+13
18
12
6
1

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The various resources listed below are aligned to the same standard, (1OA01) taken from the CCSM (Common Core Standards For Mathematics) as the Addition and subtraction Worksheet shown above.
Use addition and subtraction within 20 to solve word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions, e.g., by using objects, drawings, and equations with a symbol for the unknown number to represent the problem.
Similar to the above listing, the resources below are aligned to related standards in the Common Core For Mathematics that together support the following learning outcome:
Represent and solve problems involving addition and subtraction