Big Friends Bridge — Lesson 46a: Which way to add?
Big friends: all the adding →Lesson 46a: Which way to add on an abacus
Level 4, Big Friends Bridge. Look at the rod first. It tells you which way.
What your child does, card by card
Which way to add? Beads, small friend, or big friend? PlayBuddy opens the lesson: “First try the beads. Then the small friend. Then the big friend.”
5 + 4 = 9: four beads are free. Push them! The abacus makes 5, then clears. Here the hands lead: they show 5 and 9, and a moment later the beads copy each one. The labels “Start at 5” and “4 beads free: push = 9” light up as each idea comes. “Enough beads? Just push.” Any bead or finger may be tapped afterwards.
3 + 4 = 7: only 1 bead free. But the top bead is free. The beads show 3 and go back to zero. Here the hands lead: they show 3, 8 and 7, and a moment later the beads copy each one. On the card, “Start at 3”, “+5” and “1 back = 7” light up one by one. Then the card invites a touch: “Add 5, take 1 back.”
7 + 4 = 11: 2 beads free. The top bead is down. No room! 7 appears on the beads, then the rod clears again. Here the hands lead: they show 7, 1 and 11, and a moment later the beads copy each one. Each label lights in turn: “Start at 7”, “−6” and “+10 = 11”. After the show, the child can touch: “Take 6 off, add a ten.”
0 + 4 + 4 + 4: the abacus makes 4, 9, 8, 2 and 12 by itself, a green ring on each bead just before it moves, and the hands copy. Push. Then the small friend. Then the big friend.
In Try it a green ring marks the next bead while your child works out 1 + 3, 4 + 3 and 7 + 3, changing the beads from one number to the next.
Which way?: a mission of 8 tasks with a count of right answers in a row, with the best kept. Your child must work out 5 + 4, 3 + 4, 7 + 4, 2 + 2, 4 + 3, 8 + 3, 6 + 3 and 9 + 4.
Copy me: the hand in the lower window shows 9, 7 and 11, one at a time, and your child makes the same number on the beads.
Then the beads hide and the sums 5 + 4, 3 + 4 and 7 + 4 are done in the head, the answer shown on the fingers.
You're ready! Beads free? Push. Top bead free? Small friend. No room? Big friend.
What this lesson trains
17 answers in about five minutes. The tasks take 28 bead moves in all: 9 with a top bead and 19 with bottom beads. Up to 13, read and set from the left. Then 3 quick looks in your head. The friend rules here: +3 = +5 −2, +3 = −7 +10, +4 = +5 −1 and +4 = −6 +10, used in 7 of 11 sums.
It starts with doing: work out 1 + 3, 4 + 3 and 7 + 3.
Fingers and hands
Below the abacus the drawn hands show zero and 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 13 here, finger for bead: the left hand counts the tens, the right hand the ones.
+3 on the fingers: the thumb opens and 2 fingers close (+5 −2). +4 on the fingers: the thumb opens and one finger closes (+5 −1).
+3 on the fingers: the right hand lets 7 go and the left hand opens one more finger for the ten (−7 +10). +4 on the fingers: the right hand lets 6 go and the left hand opens one more finger for the ten (−6 +10).
On “5 + 4 = 9” 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 (9, 7 and 11); the beads answer.
What PlayBuddy and PlayType say
PlayBuddy: “First try the beads. Then the small friend. Then the big friend.”
PlayBuddy: “To add, push beads to the bar.”
PlayBuddy: “Five is one too many. So one bead goes back!”
PlayType: “Big friend off, one ten on.”
PlayBuddy: “Don't clear. The beads keep the answer.”
Stars
17 answers: 1 slip still gives three stars; up to 4, two stars.