Big Friends Bridge — Lesson 56: Big friends on the tens rod

What your child does, card by card

Big friends on the tens rod. 90 + 20, and 110 − 30. PlayType opens the lesson: “When the tens are full, the hundreds rod helps.”

Ten tens make one hundred: the tens rod is full at 9 tens. A yellow line goes round the tens rod and the hundreds rod as the kids name them. 60 appears on the beads, then the rod clears again. The labels “Full at 90” and “10 tens = 100” light up as each idea comes. “One more ten: the 9 tens go back, one bead goes up on the hundreds rod.” Any bead or finger may be tapped afterwards.

9 + 2, then 90 + 20: 2 tens: take 8 tens off, add one hundred. Yellow marks the ones rod and the tens rod while the kids talk about them. The abacus makes 9 and 90, then clears. Here the hands lead: they show 1 and 11, and a moment later the beads copy each one. On the card, “9 + 2 = 11” and “90 + 20 = 110” light up one by one. Then the card invites a touch: “The hands stop at 99. The beads do the same trick.”

First a reminder (“110 − 30”): the beads build 110, 10 and 80, ring by ring, while your child watches. Like 11 − 3: but one hundred off, then 7 tens back on.

Try it: your child works out 90 + 20, 80 + 30, 110 - 30 and 120 - 40, with a green ring on the next bead to move.

Then a short practice without rings: work out 70 + 40, 130 - 50, 95 + 10, 105 - 10 and 60 + 50, each round starting from its own number.

In your head: the abacus is covered and your child works out 90 + 20, 110 - 30 and 70 + 40, picking each answer from 80, 110 and 120.

You're ready! Big friends work on every rod: the same trick, one rod to the left.

What this lesson trains

12 answers in about five minutes. The tasks take 25 bead moves in all: 9 with a top bead and 16 with bottom beads. The largest is 130: hundreds, tens and ones. Then 3 quick looks in your head. The friend rules here: +2 = −8 +10, +3 = −7 +10, −3 = −10 +7, −4 = −10 +6, +4 = −6 +10, −5 = −10 +5, +1 = −9 +10, −1 = −10 +9 and +5 = −5 +10, used in 9 of 9 sums.

The first thing your child does: work out 90 + 20, 80 + 30, 110 - 30 and 120 - 40.

Fingers and hands

Below the abacus the drawn hands show zero and 1, 9, 10, 11, 60, 70, 80, 90 and 95 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). +3 on the fingers: the right hand lets 7 go and the left hand opens one more finger for the ten (−7 +10). −3 on the fingers: the left hand closes one finger for the ten and the right hand shows 7 more (−10 +7). −4 on the fingers: the left hand closes one finger for the ten and the right hand shows 6 more (−10 +6). +4 on the fingers: the right hand lets 6 go and the left hand opens one more finger for the ten (−6 +10). −5 on the fingers: the left hand closes one finger for the ten and the right hand shows 5 more (−10 +5). +1 on the fingers: the right hand lets 9 go and the left hand opens one more finger for the ten (−9 +10). −1 on the fingers: the left hand closes one finger for the ten and the right hand shows 9 more (−10 +9). +5 on the fingers: the right hand lets 5 go and the left hand opens one more finger for the ten (−5 +10).

Two hands hold up to 99, so past 99 they fold and fade with a note (“Our hands stop at 99. The beads go on.”) while the beads carry on.

On “9 + 2, then 90 + 20” 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.

What PlayBuddy and PlayType say

PlayType: “When the tens are full, the hundreds rod helps.”

PlayType: “The third rod is the hundreds.”

PlayType: “Big friend off, one ten on.”

PlayType: “Big friend off, one hundred on.”

PlayBuddy: “Our hands stop at ninety-nine. The beads go on.”

PlayBuddy: “One hundred off, big friend on.”

Stars

With 1 or fewer slips across the 12 answers your child earns three stars; 3 or fewer, two.