Adding and Subtracting One-Digit Numbers (8)

Example:    9 + 4 = 13 

Step 1: Set 9 on the unit rod (1^st right column). 

Step 2: Move down 1 on unit rod with the index finger, then move up 5 on unit rod with the same finger and finally move up 1 on tens’ rod (2^nd right column) with the thumb. Work the index finger and the thumb with the idea of performing the last two motions at the same time. 

Note: This example shows how to add 10 after subtracting one or more 1-unit beads and a 5-unit bead. Applicable problems:    

9+1 

9+3 

8+3 

8+4       

7+3 

6+4

Example :   13 — 4 = 9  

Step 1: Set 13. 

Step 2: After moving down the 1 on tens’ rod, move down 5 and move up 1 on unit rod at the same time.  

Note: This example shows how to add both a 5-unit bead and one or more 1-unit bead after subtracting 10. Applicable problems.     

11—2 

11—4      

12—4        

13—4

Example :   9 + 7 = 16 

Step 1: Set 9 on the unit rod. 

Step 2: Move down 3 on unit rod, and move up 1 on tens’ rod. Perform the two motions mechanically at the same time as if twisting the thumb and the index finger. 

 

Note 1: This example shows how to subtract one or more 1-unit beads from the unit rod and add Applicable problems:

2+9

4+9

6+9

8+9

9+9

Example :    16 - 7 = 9 

Step 1: Set 16. 

Step 2: Move down the 1 on tens’ rod, and move up 3 on unit rod.  

Note 1: When setting a two-digit number on the board, as in Step 1, always set the tens’ digit first. 

Note 2: This example shows how to subtract 10 and add one or more 1-unit beads. Applicable problems:    

15—6  

16—7  

17—8 

17—9         

18—9