Lesson 107: Abacus two-digit flash sums practice
Level 9, Mind Castle. Two-digit columns on the beads, then flash sums. Beat your best time!
What your child does, card by card
Two-digit flash practice. Practice day! PlayBuddy opens the lesson: “Practice time. Let's get quicker and better.”
Fast columns: a mission of 6 tasks with a clock against your child’s own best time. Your child must work out the columns 23 + 14 + 31, 56 - 21 + 12 and 18 + 27 + 33.
Flash sums in your head: the abacus is covered and the numbers appear one at a time, 1.4 seconds each (21 + 14, 35 + 22 - 16, 40 + 25 + 13 and 17 + 32 + 24); your child adds them in the head and picks the total from 35, 41, 73 and 78.
You're ready! Two-digit flash sums, quick and calm.
What this lesson trains
10 answers, roughly five minutes: 17 moves of the beads, 4 of them with the top bead and 13 with bottom beads. Up to 78, read and set from the left. Then 4 quick looks in your head. 5 of the 6 sums need a friend (“+4 = +5 −1”, “+3 = +5 −2”, “−2 = −5 +3” and “+7 = −3 +10”); the others use free beads.
The sum sheet
The lower window shows the column as a child would write it on paper: one number under another, the current line in yellow, ticks on the lines done. The abacus carries the running total from line to line.
What PlayBuddy and PlayType say
PlayBuddy: “Practice time. Let's get quicker and better.”
PlayBuddy: “Click Let's Begin, or press Enter!”
PlayBuddy: “Here comes the last one.”
PlayType: “Now do it in your head.”
Stars
10 answers: 1 slip still gives three stars; up to 2, two stars.