Lesson 19: Three-number sums on an abacus
Level 2, Easy Street. One step at a time. Never clear in between.
What your child does, card by card
Three numbers in a row. Add, then take away. PlayType opens the lesson: “Three numbers in one sum. One step at a time.”
1 + 3 − 2 = 2: the beads keep the answer of each step. 1 appears on the beads, then the rod clears again. On the card, “1”, “+ 3 = 4” and “− 2 = 2” light up one by one. Then the card invites a touch: “Tap a bead to try it.”
First a reminder (“2 + 5 − 1”): the beads build 2, 7 and 6, ring by ring, while your child watches. Add 5, then take away 1. No clearing.
Try it: your child works out 1 + 3, 4 - 2, 2 + 5 and 7 - 1, with a green ring on the next bead to move, changing the beads from one number to the next.
Then a short practice without rings: work out 3 + 1, 4 - 2, 2 + 5, 7 - 2 and 5 - 5; the beads are never cleared in between.
Then the beads hide and the sums 1 + 3 - 1, 2 + 5 - 1 and 4 - 3 + 1 are done in the head, the answer shown on the fingers.
You're ready! You can do three numbers in a row.
What this lesson trains
About five minutes and 12 answers. Altogether the child makes 9 bead moves (3 with the top bead, 6 with bottom beads). 1 of them is a clear. 7 is the top number here. Then 3 quick looks in your head.
It starts with doing: work out 1 + 3, 4 - 2, 2 + 5 and 7 - 1.
Fingers and hands
Below the abacus the drawn hands show zero and 1, 2, 3, 4, 5, 6 and 7 here, finger for bead.
What PlayBuddy and PlayType say
PlayType: “Three numbers in one sum. One step at a time.”
PlayBuddy: “Don't clear. The beads keep the answer.”
Stars
12 answers: 1 slip still gives three stars; up to 3, two stars.