Column Tower — Lesson 71: Column sums: three numbers
Columns of four and five numbers →Lesson 71: Abacus column sums for kids: three numbers
Level 6, Column Tower. Like lesson 19, written top to bottom. The hands rest: the sum sheet shows your place.
What your child does, card by card
Column sums: three numbers. A tower of three numbers. PlayType opens the lesson: “A column sum is a tower of numbers.”
7 + 8 − 5: top to bottom: set 7, add 8, take away 5. The beads work the column line by line, 7, 15 and 10, while the sum sheet below lights each line and ticks it; “Start: 7”, “+ 8 = 15” and “− 5 = 10” light up as the total grows. A line with − means take away.
9 + 6 + 7: the abacus makes 9, 5, 15, 17, 12 and 22 by itself, a green ring on each bead just before it moves, and the sum sheet below ticks each line. The beads keep the answer. Never clear in the middle.
In Try it a green ring marks the next bead while your child works out the columns 7 + 8 - 5 and 5 + 9 + 6.
The tiny practice drops the ring: work out the columns 8 - 3 + 7, 9 + 9 - 4 and 6 + 7 + 8, each round starting from its own number.
In your head: the abacus is covered and your child works out 3 + 4 + 2, 5 + 2 - 1 and 6 + 3 - 4, picking each answer from 5, 6 and 9.
You're ready! A column is done one line at a time.
What this lesson trains
13 answers, roughly five minutes: 21 moves of the beads, 5 of them with the top bead and 16 with bottom beads. The largest is 21: tens and ones. Then 3 quick looks in your head. 8 of the 10 sums need a friend (“+8 = −2 +10”, “+9 = +4 −5 +10”, “+6 = −4 +10”, “+7 = +2 −5 +10”, “+9 = −1 +10” and “−4 = −5 +1”); the others use free beads.
Your child’s first moves: work out the columns 7 + 8 - 5 and 5 + 9 + 6.
The sum sheet
Below the abacus a sum sheet replaces the hands: it writes the column out, lights the line your child is on and ticks each line done; the total appears after the last line. The beads hold the running total the whole way down.
What PlayBuddy and PlayType say
PlayType: “A column sum is a tower of numbers.”
PlayBuddy: “One line at a time, top to bottom.”
PlayBuddy: “Don't clear. The beads keep the answer.”
Stars
Three stars for up to 1 slip in 13 answers, two stars for up to 3. A number counts as a slip only when it stays wrong for a moment and is not on the way to the answer, so a child who moves beads one at a time is never marked down. After two slips on one task the green ring comes back.
About Column Tower
Column Tower is Level 6 of nine (grade 3): 3 to 10 lines, 1 to 3 digits, adding and taking away. In your head: flash sums start.