Mix Mountain — Lesson 68: All the friends: three-digit sums

What your child does, card by card

All the friends: three-digit sums. Practice day! PlayBuddy opens the lesson: “Practice time. Let's get quicker and better.”

First a reminder (“25 + 37: tens first, then ones”): the beads build 25, 75, 55, 57, 52 and 62, ring by ring, while your child watches. Add 3 tens. Then 7 ones, with the friend it needs.

Try it: your child works out 56 + 28, 62 - 38, 213 + 145 and 125 + 137, with a green ring on the next bead to move.

Five in a row: a mission of 8 tasks with a count of right answers in a row, with the best kept. Your child must work out 125 + 137, 379 + 145, 408 + 196, 256 + 368, 624 - 368, 503 - 247, 812 - 456 and 345 + 278.

Copy me: the beads show 62, 24 and 56 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 30 + 45, 68 - 23 and 125 + 100, picking each answer from 45, 75 and 225.

You're ready! Three-digit sums with every friend.

What this lesson trains

18 answers, roughly five minutes: 78 moves of the beads, 29 of them with the top bead and 49 with bottom beads. Up to 812, read and set from the left. Then 3 quick looks in your head. 12 of the 12 sums need a friend (“+8 = +3 −5 +10”, “−3 = −5 +2”, “−8 = −10 +2”, “+4 = +5 −1”, “+3 = +5 −2”, “+7 = +2 −5 +10”, “+4 = −6 +10”, “+5 = −5 +10”, “+1 = +5 −4”, “+6 = +1 −5 +10”, “−6 = −10 +5 −1”, “−8 = −10 +5 −3”, “−2 = −5 +3”, “−4 = −10 +6”, “−7 = −10 +5 −2”, “−4 = −5 +1”, “−5 = −10 +5”, “+2 = +5 −3” and “+7 = −3 +10”); the others use free beads.

Your child’s first moves: work out 56 + 28, 62 - 38, 213 + 145 and 125 + 137.

Fingers and hands

Below the abacus the drawn hands show zero and 24, 56, 62 and 84 here, finger for bead: the left hand counts the tens, the right hand the ones.

−3 on the fingers: the thumb closes and 2 fingers open (−5 +2). +4 on the fingers: the thumb opens and one finger closes (+5 −1). +3 on the fingers: the thumb opens and 2 fingers close (+5 −2). +1 on the fingers: the thumb opens and 4 fingers close (+5 −4). −2 on the fingers: the thumb closes and 3 fingers open (−5 +3). −4 on the fingers: the thumb closes and one finger opens (−5 +1). +2 on the fingers: the thumb opens and 3 fingers close (+5 −3).

+8 on the fingers: the right hand opens 3 fingers and folds the thumb, then the left hand opens one more finger for the ten (+3 −5 +10). −8 on the fingers: the left hand closes one finger for the ten and the right hand shows 2 more (−10 +2). +7 on the fingers: the right hand opens 2 fingers and folds the thumb, then the left hand opens one more finger for the ten (+2 −5 +10). +4 on the fingers: the right hand lets 6 go and the left hand opens one more finger for the ten (−6 +10). +5 on the fingers: the right hand lets 5 go and the left hand opens one more finger for the ten (−5 +10). +6 on the fingers: the right hand opens one finger and folds the thumb, then the left hand opens one more finger for the ten (+1 −5 +10). −6 on the fingers: the left hand closes one finger for the ten, then the right hand puts the thumb out and closes one finger (−10 +5 −1). −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). −4 on the fingers: the left hand closes one finger for the ten and the right hand shows 6 more (−10 +6). −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). −5 on the fingers: the left hand closes one finger for the ten and the right hand shows 5 more (−10 +5). +7 on the fingers: the right hand lets 3 go and the left hand opens one more finger for the ten (−3 +10).

Above 99 the drawn hands rest, faded, because ten fingers stop at 99; the abacus keeps going.

In Copy me the beads lead with 62, 24 and 56, and your child answers on the fingers: the reverse of making a number on the beads.

What PlayBuddy and PlayType say

PlayBuddy: “Practice time. Let's get quicker and better.”

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

PlayType: “First the tens, and then the ones.”

PlayBuddy: “Here comes the last one.”

Stars

Three stars for up to 1 slip in 18 answers, two stars for up to 4.