1. Direct subtraction
If the beads you need to remove are already touching the beam, just move them away.
Example: 8 − 3 = 5. 8 is the heaven bead plus three earth beads. Pull the three earth beads down, leaving 5.
2. Subtracting with small friends
Rule: to take away a number, take away 5 and add back its small friend.
Example: 6 − 3 = 3. 6 is the heaven bead plus one earth bead, so we cannot remove three earth beads. Take away 5 (push the heaven bead up) and add 2 (the small friend of 3). The rod shows 3.
3. Subtracting with big friends
Rule: to take away a number, take away 10 from the next rod and add back its big friend.
Example: 12 − 5 = 7. The ones rod shows 2, which is too small. Take 1 from the tens rod (−10) and add 5 (the big friend of 5) to the ones rod. Answer: 7.
Try it yourself
Show 13, then take away 7 using big friends: −10, then +3.
Your abacus shows 0.
Quick check
Type your answers, then check them. Get them all right to complete the lesson automatically.
Practice tips
- Subtraction is addition in reverse. If you know the addition move, flip it.
- Check every answer by adding the number back. You should return to where you started.