Big Friends Bridge — Lesson 48: Big friends: minus 9
Big friends: minus 8 →Lesson 48: Big friends minus 9 on an abacus
Level 4, Big Friends Bridge. Take one ten away. The big friend comes back.
What your child does, card by card
Big friends: minus 9. Not enough ones? A ten helps. PlayType opens the lesson: “Not enough beads to take away nine. Borrow a ten.”
3 + 9 = 12: a ten is 1 too many. Take 1 off first. 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. “Start at 3”, “−1” and “+10 = 12” glow on the card in step with the beads. The card ends on a touch: “Now we go back the same way.”
19 − 9, then 12 − 9: 19 − 9: nine ones are there. Take them! A yellow line goes round the ones rod as the kids name it. 19 and 12 appear on the beads, then the rod clears again. Above, “19 − 9: 9 ones there” and “12 − 9: only 2 ones” take turns to glow. Its words: “12 − 9: only 2 ones. Not enough!”
Take a ten, give 1 back: 10 is 9 and 1. Taking a ten is 1 too many. Yellow marks the tens rod while the kids talk about it. The abacus makes 12, then clears. Here the hands lead: they show 12, 2 and 3, and a moment later the beads copy each one. The labels “−10: one ten”, “1 too many: 1 bead back on” and “3” light up as each idea comes. “3 again! That is where 3 + 9 began.” Any bead or finger may be tapped afterwards.
Minus 9: one ten off, 1 on: one bead off the tens rod. The big friend, 1, comes to the bar. On this card “−10: one ten”, “+1: the big friend” and “−9 = −10 +1” glow in turn as the beads move. Your child copies the order to work out 12 - 9 and 16 - 9.
Try it: your child works out 10 - 9, 13 - 9 and 17 - 9, with a green ring on the next bead to move.
Then a short practice without rings: work out 11 - 9, 18 - 9, 19 - 9, 15 - 9 and 12 - 9, each round starting from its own number.
In Copy me the drawn hand holds up 3, 7 and 1 in turn, and your child copies each one in beads.
In your head: the abacus is covered and your child works out 12 - 9, 16 - 9 and 10 - 9, showing each answer on the drawn fingers.
You're ready! Not enough ones to take 9? Take a ten, give 1 back.
What this lesson trains
About five minutes and 16 answers. Altogether the child makes 24 bead moves (2 with the top bead, 22 with bottom beads). Numbers reach 19, so the tens rod and the ones rod work. Then 3 quick looks in your head. 9 of the 10 sums need a big friend (“−9 = −10 +1”); the others use free beads.
It starts with doing: work out 10 - 9, 13 - 9 and 17 - 9.
Fingers and hands
Below the abacus the drawn hands show zero and 1, 2, 3, 4, 6, 7, 8, 9, 10, 11, 12, 13, 15, 16, 17, 18 and 19 here, finger for bead: the left hand counts the tens, the right hand the ones.
−9 on the fingers: the left hand closes one finger for the ten and the right hand shows 1 more (−10 +1).
On “3 + 9 = 12” 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.
In Copy me the hand leads with 3, 7 and 1 and your child turns each into beads.
What PlayBuddy and PlayType say
PlayType: “Not enough beads to take away nine. Borrow a ten.”
PlayType: “Ten is one too many. So take one off first, then add the ten!”
PlayType: “To take away, move beads off the bar.”
PlayBuddy: “Taking ten is one too many. So one bead comes back!”
Stars
16 answers: 1 slip still gives three stars; up to 4, two stars.