Lesson 39: Big friends plus 9 on an abacus
Level 4, Big Friends Bridge. When a rod has no room, the big friend helps.
What your child does, card by card
Big friends: plus 9. 3 + 9. Where do 9 more beads go? PlayBuddy opens the lesson: “I want to add nine, but this rod is too full.”
9 and 1 make 10: one bead on the tens rod is 9, and 1 more. The beads show 9, 8 and 7 and go back to zero. On the card, “9 and 1”, “8 and 2” and “7 and 3” light up one by one. Then the card invites a touch: “You found the friends of 10 last time.”
Find the friend of 10: the beads show 9 and 8 in turn and hold still, and your child shows each one's friend on the drawn fingers, so 9 and 1 and 8 and 2 each make 10.
3 + 9, one by one: 6 more fill the rod. Then 3 more: 10, 11, 12. Yellow marks the ones rod and the tens rod while the kids talk about them. The abacus makes 3, then clears. “6 more: full at 9” and “3 more: 12” glow on the card in step with the beads. The card ends on a touch: “It works. But it is slow.”
Add a ten, take 1 off: 10 is 9 and 1. So a ten is 1 too many. The tens rod is outlined in yellow while the kids explain. The beads show 3 and go back to zero. Here the hands lead: they show 3, 2 and 12, and a moment later the beads copy each one. Above, “+ 9? No room”, “−1 first” and “+10 = 12” take turns to glow. Its words: “12 again! The same as counting.”
Plus 9: 1 off, one ten on: take the big friend, 1, off. Then one bead on the tens rod. First the abacus shows the rule bead by bead (“−1: the big friend”, “+10: one ten” and “+9 = −1 +10”). Next it is your child's turn: work out 3 + 9 and 7 + 9, the ring marking the top bead before the friend.
Try it puts a green ring on each next bead; your child works out 1 + 9, 4 + 9 and 8 + 9.
A tiny practice with no ring: work out 3 + 9, 0 + 9, 2 + 9, 6 + 9 and 9 + 9, each round starting from its own number.
Copy me: the hand in the lower window shows 12, 16 and 10, one at a time, and your child makes the same number on the beads.
Then the beads hide and the sums 3 + 9, 7 + 9 and 1 + 9 are done in the head, the answer shown on the fingers.
You're ready! No room for 9? Take 1 off, add a ten.
What this lesson trains
18 answers, roughly five minutes: 26 moves of the beads, 2 of them with the top bead and 24 with bottom beads. Numbers reach 18, so the tens rod and the ones rod work. Then 3 quick looks in your head. The friend rules here: +9 = −1 +10, used in 9 of 10 sums.
It starts with doing: work out 1 + 9, 4 + 9 and 8 + 9.
Fingers and hands
In the lower window two drawn hands work as a finger abacus and always match the beads: a finger up is a bottom bead (1), the thumb out is the top bead (5), a closed hand is zero. In this lesson the hands show zero and 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 15, 16, 17 and 18.
+9 on the fingers: the right hand lets 1 go and the left hand opens one more finger for the ten (−1 +10).
On “Add a ten, take 1 off” the hands move first and the beads follow, so your child sees that a finger and a bead move together: open a finger and a bead goes to the bar, close it and the bead goes back.
The fingers lead in Copy me (12, 16 and 10); the beads answer.
What PlayBuddy and PlayType say
PlayBuddy: “I want to add nine, but this rod is too full.”
PlayBuddy: “Nine and one. Eight and two. Seven and three.”
PlayBuddy: “Seven, eight, nine. Every bead is on the bar. This rod is full!”
PlayType: “One more? There is no room! So the nine beads go back, and one bead goes up on the next rod.”
PlayType: “Ten is one too many. So take one off first, then add the ten!”
Stars
18 answers: 1 slip still gives three stars; up to 4, two stars. A number counts as a slip only when it stays wrong for a moment and is not on the way to the answer, so a child who moves beads one at a time is never marked down. After two slips on one task the green ring comes back.
About Big Friends Bridge
Big Friends Bridge is Level 4 of nine (grade 2): +9 to +1 and −9 to −1 with the next rod and a big friend. In your head: big friend sums in your head.