Big friends on an abacus
Big friends are buddy numbers that make 10. When a rod is full, add 1 to the rod on the left (+10) and take away the buddy number!
| Move | Formula | Use it when |
|---|---|---|
| +1 | +1 = +10 −9 | The rod is full: add 1 to the rod on the left, then take away the buddy number |
| +2 | +2 = +10 −8 | The rod is full: add 1 to the rod on the left, then take away the buddy number |
| +3 | +3 = +10 −7 | The rod is full: add 1 to the rod on the left, then take away the buddy number |
| +4 | +4 = +10 −6 | The rod is full: add 1 to the rod on the left, then take away the buddy number |
| +5 | +5 = +10 −5 | The rod is full: add 1 to the rod on the left, then take away the buddy number |
| +6 | +6 = +10 −4 | The rod is full: add 1 to the rod on the left, then take away the buddy number |
| +7 | +7 = +10 −3 | The rod is full: add 1 to the rod on the left, then take away the buddy number |
| +8 | +8 = +10 −2 | The rod is full: add 1 to the rod on the left, then take away the buddy number |
| +9 | +9 = +10 −1 | The rod is full: add 1 to the rod on the left, then take away the buddy number |
| −1 | −1 = −10 +9 | Not enough beads: take 1 from the left rod, then add the buddy number |
| −2 | −2 = −10 +8 | Not enough beads: take 1 from the left rod, then add the buddy number |
| −3 | −3 = −10 +7 | Not enough beads: take 1 from the left rod, then add the buddy number |
| −4 | −4 = −10 +6 | Not enough beads: take 1 from the left rod, then add the buddy number |
| −5 | −5 = −10 +5 | Not enough beads: take 1 from the left rod, then add the buddy number |
| −6 | −6 = −10 +4 | Not enough beads: take 1 from the left rod, then add the buddy number |
| −7 | −7 = −10 +3 | Not enough beads: take 1 from the left rod, then add the buddy number |
| −8 | −8 = −10 +2 | Not enough beads: take 1 from the left rod, then add the buddy number |
| −9 | −9 = −10 +1 | Not enough beads: take 1 from the left rod, then add the buddy number |
Mixed friends
Some moves need both friends: add 10 on the left rod first, then use the 5 bead on the ones rod.
| Move | Formula | Use it when |
|---|---|---|
| +6 | +6 = +10 −5 +1 | Add 10 on the left rod first, then use the 5 bead on this rod |
| +7 | +7 = +10 −5 +2 | Add 10 on the left rod first, then use the 5 bead on this rod |
| +8 | +8 = +10 −5 +3 | Add 10 on the left rod first, then use the 5 bead on this rod |
| +9 | +9 = +10 −5 +4 | Add 10 on the left rod first, then use the 5 bead on this rod |
| −6 | −6 = −10 +5 −1 | Take 10 from the left rod, then use the 5 bead to finish |
| −7 | −7 = −10 +5 −2 | Take 10 from the left rod, then use the 5 bead to finish |
| −8 | −8 = −10 +5 −3 | Take 10 from the left rod, then use the 5 bead to finish |
| −9 | −9 = −10 +5 −4 | Take 10 from the left rod, then use the 5 bead to finish |
Questions
How do big friends (+10) work?
Big friends are buddy numbers that add up to 10: (1 and 9), (2 and 8), (3 and 7), (4 and 6), and (5 and 5). When a rod is full, add 1 to the rod on the left (+10) and take away the buddy number! For example: +9 = +10 − 1.