Big Friends Bridge — Lesson 40: Big friends: plus 8
Plus 9 and plus 8 practice →Lesson 40: Big friends plus 8 on an abacus
Level 4, Big Friends Bridge. Plus 8: take 2 off, add a ten.
What your child does, card by card
Big friends: plus 8. 8 and 2 make 10. PlayType opens the lesson: “Same trick, new friend.”
4 + 9 = 13: a ten is 1 too many. Take 1 off first. The abacus makes 4, then clears. Here the hands lead: they show 4, 3 and 13, and a moment later the beads copy each one. The labels “−1” and “+10 = 13” light up as each idea comes. “The trick of lesson 39.” Any bead or finger may be tapped afterwards.
4 + 8: only 5 more fit on this rod. The ones rod is outlined in yellow while the kids explain. The beads show 4 and go back to zero. On the card, “Start at 4” and “+ 8? Only 5 fit” light up one by one. Then the card invites a touch: “8 will not fit. So add a ten!”
Plus 8: 2 off, one ten on: 10 is 8 and 2. So a ten is 2 too many. First the abacus shows the rule bead by bead (“−2: the big friend”, “+10: one ten” and “+8 = −2 +10”). Next it is your child's turn: work out 4 + 8 and 3 + 8, the ring marking the top bead before the friend.
Try it puts a green ring on each next bead; your child works out 2 + 8, 7 + 8 and 9 + 8.
A tiny practice with no ring: work out 3 + 8, 8 + 8, 1 + 8, 4 + 8 and 2 + 8, each round starting from its own number.
In Copy me the drawn hand holds up 12, 11 and 10 in turn, and your child copies each one in beads.
In your head: the abacus is covered and your child works out 4 + 8, 7 + 8 and 9 + 8, showing each answer on the drawn fingers.
You're ready! No room for 8? Take 2 off, add a ten.
What this lesson trains
About five minutes and 16 answers. Altogether the child makes 25 bead moves (1 with the top bead, 24 with bottom beads). Up to 17, read and set from the left. Then 3 quick looks in your head. 9 of the 10 sums need a big friend (“+8 = −2 +10”); the others use free beads.
Your child’s first moves: work out 2 + 8, 7 + 8 and 9 + 8.
Fingers and hands
Below the abacus the drawn hands show zero and 1, 2, 3, 4, 7, 8, 9, 10, 11, 12, 13, 15, 16 and 17 here, finger for bead: the left hand counts the tens, the right hand the ones.
+8 on the fingers: the right hand lets 2 go and the left hand opens one more finger for the ten (−2 +10).
On “4 + 9 = 13” 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.
Copy me turns it round: 12, 11 and 10 appear on the hand first.
What PlayBuddy and PlayType say
PlayType: “Ten is one too many. So take one off first, then add the ten!”
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.