Mix Mountain — Lesson 63: The mix: minus 7, minus 8 and minus 9

What your child does, card by card

The mix: minus 7, minus 8 and minus 9. 7, 8 and 9 are five and some more. PlayType opens the lesson: “Same trick, new friend.”

−7 = −10 +5 −2: 7 is 5 and 2. The 5 first, then the 2. First the abacus shows the rule bead by bead (“−10: one ten off”, “+5: top bead on” and “−2: two beads down”). Next it is your child's turn: work out 13 - 7, 13 - 8 and 14 - 9, the ring marking the top bead before the friend.

First a reminder (“14 − 8, then 14 − 9”): the beads build 14, 4, 9, 6, 14, 4, 9 and 5, ring by ring, while your child watches. 8 is 5 and 3. 9 is 5 and 4.

Try it: your child works out 12 - 7, 14 - 8 and 24 - 9, with a green ring on the next bead to move.

Then a short practice without rings: work out 14 - 7, 11 - 8, 13 - 8, 22 - 7 and 14 - 9, each round starting from its own number.

In Copy me the drawn hand holds up 6, 5 and 7 in turn, and your child copies each one in beads.

In your head: the abacus is covered and your child works out 13 - 7, 14 - 8 and 14 - 9, picking each answer from 5, 6 and 7.

You're ready! Minus 7, 8 and 9: the five first, then the small part.

What this lesson trains

17 answers in about five minutes. The tasks take 37 bead moves in all: 13 with a top bead and 24 with bottom beads. Numbers reach 24, so the tens rod and the ones rod work. Then 3 quick looks in your head. Friends do 11 of the 11 sums, by −7 = −10 +5 −2, −8 = −10 +5 −3, −9 = −10 +5 −4 and −8 = −10 +2.

It starts with doing: work out 12 - 7, 14 - 8 and 24 - 9.

Fingers and hands

Below the abacus the drawn hands show zero and 3, 5, 6, 7, 8, 9, 11, 12, 13, 14, 15, 22 and 24 here, finger for bead: the left hand counts the tens, the right hand the ones.

−7 on the fingers: the left hand closes one finger for the ten, then the right hand puts the thumb out and closes 2 fingers (−10 +5 −2). −8 on the fingers: the left hand closes one finger for the ten, then the right hand puts the thumb out and closes 3 fingers (−10 +5 −3). −9 on the fingers: the left hand closes one finger for the ten, then the right hand puts the thumb out and closes 4 fingers (−10 +5 −4). −8 on the fingers: the left hand closes one finger for the ten and the right hand shows 2 more (−10 +2).

On “The mix: minus 7, minus 8 and minus 9” 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 hand leads with 6, 5 and 7 and your child turns each into beads.

What PlayBuddy and PlayType say

PlayType: “Same trick, new friend.”

PlayBuddy: “Click Let's Begin, or press Enter!”

PlayBuddy: “Now watch the hands closely.”

PlayBuddy: “Here comes the last one.”

Stars

17 answers: 1 slip still gives three stars; up to 4, two stars.