Column Tower — Lesson 78: Mixed column practice

What your child does, card by card

Mixed column practice. Practice day! PlayBuddy opens the lesson: “Practice time. Let's get quicker and better.”

108 + 47 − 9: the abacus makes 108, 148, 145, 195, 155, 105, 145 and 146 by itself, a green ring on each bead just before it moves, and the sum sheet below ticks each line. Left to right on every line, whatever its size.

In Try it a green ring marks the next bead while your child works out the column 26 + 8 - 13.

Fast sums: a mission of 9 tasks with a clock against your child’s own best time. Your child must work out the columns 7 + 58 - 23, 342 - 26 + 9, 65 + 128 - 47 and 9 + 8 + 7 + 6.

Then the beads hide and the sums 8 + 12 + 5, 30 + 7 - 5 and 100 + 50 + 5 are done in the head, the answer picked from 25, 32 and 155.

You're ready! Columns of every size.

What this lesson trains

14 answers in about five minutes. The tasks take 35 bead moves in all: 9 with a top bead and 26 with bottom beads. The largest is 342: hundreds, tens and ones. Then 3 quick looks in your head. The friend rules here: +8 = +3 −5 +10, +8 = −2 +10, −2 = −5 +3, −3 = −5 +2, −6 = −10 +5 −1, +9 = −1 +10, −7 = −10 +5 −2, +7 = +2 −5 +10 and +6 = −4 +10, used in 10 of 11 sums.

Your child’s first moves: work out the column 26 + 8 - 13.

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

PlayBuddy: “One line at a time, top to bottom.”

Stars

Three stars for up to 1 slip in 14 answers, two stars for up to 3.