Lesson 21: Two-digit subtraction on an abacus
Level 2, Easy Street. Take away the tens first, then the ones.
What your child does, card by card
Taking away tens and ones. 87 − 25, and more. PlayType opens the lesson: “Now take away tens and ones. Tens go first.”
87 − 25 = 62: take away 2 tens, then 5 ones. Yellow marks the tens rod and the ones rod while the kids talk about them. The abacus makes 87, then clears. Here the hands lead: they show 67 and 62, and a moment later the beads copy each one. Above, “Start at 87”, “− 20 = 67” and “− 5 = 62” take turns to glow. Its words: “We say twenty-five: tens first.”
Watch me: 96, 56 and 55 appear on the beads one move at a time, each bead ringed in green before it goes. 4 tens first, then 1 one.
Try it puts a green ring on each next bead; your child works out 87 - 25, 96 - 41 and 68 - 13.
A tiny practice with no ring: work out 79 - 24, 77 - 52, 48 - 31 and 99 - 99, each round starting from its own number.
Copy me: the beads show 62, 35 and 17 and your child answers by tapping the drawn fingers, the hands window glowing.
In your head: the abacus is covered and your child works out 87 - 25, 75 - 25 and 43 - 22, showing each answer on the drawn fingers.
You're ready! You can take away tens and ones.
What this lesson trains
13 answers in about five minutes. The tasks take 16 bead moves in all: 4 with a top bead and 12 with bottom beads. 1 of the 10 bead tasks end on zero. Up to 99, read and set from the left. Then 3 quick looks in your head.
The first thing your child does: work out 87 - 25, 96 - 41 and 68 - 13.
Fingers and hands
Below the abacus the drawn hands show zero and 17, 23, 25, 35, 48, 55, 62, 67, 68, 77, 79, 87, 96 and 99 here, finger for bead: the left hand counts the tens, the right hand the ones.
On “87 − 25 = 62” 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.
In Copy me the beads lead with 62, 35 and 17, and your child answers on the fingers: the reverse of making a number on the beads.
What PlayBuddy and PlayType say
PlayType: “Now take away tens and ones. Tens go first.”
Stars
With 1 or fewer slips across the 13 answers your child earns three stars; 3 or fewer, two.