Addition and subtraction: facts to 18
1 Addition fact to 18 
2 Add three numbers 
3 Addition with a missing number
4 Subtraction fact to 18
5 Subtract three numbers
6 Subtraction with a missing number
7 Check-up (1) 
8 Word problem: addition to 18
9 Word problem: subtraction to 18
10 Check-up (2)
11 Check-up (3)