Skill 18A
Doubles Fact Families

There are 4 choices below.
Which one is a "doubles fact family"?

a.   b.  

4

+ 14

18

 

14

-  4

10

 

12

-  5

7

 

5

+ 12

17

 
c.   d.  

7

+ 7

14

 

14

-  7

7

 

not sure