Big Friends Bridge — Lesson 46: Big friends: plus 2 and plus 1
Which way to add? →Lesson 46: Big friends plus 2 and plus 1 on an abacus
Level 4, Big Friends Bridge. The last two big friends.
What your child does, card by card
Big friends: plus 2 and plus 1. 2 and 8 make 10. 1 and 9 make 10. PlayType opens the lesson: “Same trick, new friend.”
9 + 1: you know this one!: lesson 7: the nine beads go back, one ten goes on. Yellow marks the ones rod and the tens rod while the kids talk about them. The abacus makes 6, then clears. On the card, “−9: the big friend”, “+10: one ten” and “+1 = −9 +10” light up one by one. Then the card invites a touch: “Plus 1: take 9 off, add a ten.”
9 + 2: the rod is full. Nothing fits. The ones rod is outlined in yellow while the kids explain. The beads show 9 and go back to zero. Each label lights in turn: “Start at 9” and “+ 2? The rod is full”. After the show, the child can touch: “So add a ten!”
Plus 2: 8 off, one ten on: 10 is 2 and 8. So a ten is 8 too many. First the abacus shows the rule bead by bead (“−8: the big friend”, “+10: one ten” and “+2 = −8 +10”). Next it is your child's turn: work out 9 + 2 and 8 + 2, the ring marking the top bead before the friend.
First a reminder (“19 + 1 = 20”): the beads build 19, 10 and 20, ring by ring, while your child watches. The nine beads go back. The new ten joins the ten that is there.
Try it: your child works out 9 + 1, 8 + 2 and 9 + 2, with a green ring on the next bead to move.
Then a short practice without rings: work out 9 + 1, 8 + 2, 2 + 2, 9 + 2 and 19 + 1, each round starting from its own number.
Copy me: the hand in the lower window shows 10, 11 and 20, one at a time, and your child makes the same number on the beads.
Then the beads hide and the sums 9 + 1, 8 + 2 and 9 + 2 are done in the head, the answer shown on the fingers.
You're ready! Plus 2: take 8 off. Plus 1: take 9 off. Then add a ten.
What this lesson trains
About five minutes and 16 answers. Altogether the child makes 32 bead moves (9 with the top bead, 23 with bottom beads). Up to 20, read and set from the left. Then 3 quick looks in your head. 9 of the 10 sums need a big friend (“+2 = −8 +10” and “+1 = −9 +10”); the others use free beads.
Your child’s first moves: work out 9 + 1, 8 + 2 and 9 + 2.
Fingers and hands
Below the abacus the drawn hands show zero and 2, 4, 6, 8, 9, 10, 11, 19 and 20 here, finger for bead: the left hand counts the tens, the right hand the ones.
+2 on the fingers: the right hand lets 8 go and the left hand opens one more finger for the ten (−8 +10). +1 on the fingers: the right hand lets 9 go and the left hand opens one more finger for the ten (−9 +10).
In Copy me the hand leads with 10, 11 and 20 and your child turns each into beads.
What PlayBuddy and PlayType say
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.”
PlayBuddy: “No room on this rod. Ask the big friend.”
Stars
Three stars for up to 1 slip in 16 answers, two stars for up to 4.