Smart Starters · Ages 8 to 10
Mixed Number Speed Dash
Race between frozen research stations by adding and subtracting mixed numbers against a friendly timer, for ages 8 to 10.
5 levels+40 XP
ProgressNot started
5 levels · BeginnerPlay
Smart Starters · Ages 8 to 10
All Smart Starters gamesColumn Sub Borrow Bank
Three-digit column subtraction with borrowing, including borrowing across a zero. For ages 8 to 10.
PuzzleThree digit column subtraction with borrowing across zeros~11 min per level5 levelsAll devices
- Free · no account required
- COPPA compliant
- +10 XP per level
- 5 levels
- Plays on all devices
- Curriculum-aligned
The learning journey
Every activity is one step. Here is where this one fits.
- Play(you are here)Learn the idea in a game
- PractiseLock it in on paper
- ReviewCome back and keep it sharp
- MasterTake on a harder challenge
- AchieveEarn a certificate
About Column Sub Borrow Bank
Column Sub Borrow Bank is the case that breaks children who have been borrowing by habit. Taking 128 from 305 begins normally: five is smaller than eight, so a ten is needed from the column to the left — except that column is empty. The borrow has to travel further, taking a hundred, turning the empty tens column into nine, and only then giving the ones what they need, so 305 is rewritten as 2 hundreds, 9 tens and 15 ones. Every zero the borrow passes becomes a nine, and that cascade is why borrowing across zeros is taught as its own case rather than left to be discovered. Children who have learned the two-digit version as a fixed sequence of moves usually try to take a ten from a column that has none, produce a nine from nowhere without knowing why, or simply subtract the smaller digit from the larger and move on. Writing the fully exchanged number down before subtracting is what makes the cascade visible instead of something to be held in the head, and it is why this game has the child place the whole rewritten row. This extends our Column Sub Exchange Cave for younger children, which does the same method at two digits with a single exchange. The first two levels display the exchanged row so the child can see what happened; from the third they produce it, and a zero is forced into the tens so the hard case is met rather than avoided. Free, no sign-up, no advertising to children.
Where to go next
Chosen by the skills this activity practises.
Next — more of the same skill
Printable worksheets for this skill
A hand for grown-ups
- Before you start
- Objects to take away make subtraction concrete — start with a small pile they can physically remove from.
- While they work
- For "8 − 3", some children count back and some count up from 3 to 8. Both are correct; let them use whichever they find easier.
- Afterwards
- Talk about "how many are left" and "how many more" in real situations — they are the same idea wearing different words.
- Watch out for
- Subtracting the smaller digit from the larger out of habit in column sums (e.g. 41 − 8 giving 47). Point back to which number is on top.
- Away from the screen
- Eat some of a snack pile and ask how many are left. Spend pretend money and work out the change.
How to play
A question appears on screen
A maths question is shown in large text at the centre of the play area. A timer bar begins counting down from 160 seconds.
Choose the correct answer
Answer options are shown as large buttons. Tap and drag, or use the mouse on desktop. Any input method works — touch, mouse or keyboard.
Build your streak
Each consecutive correct answer increases your streak. A longer streak lights up the flame icon and adds a bonus multiplier to the XP you earn for the level.
Finish the level
Each level has 4 questions. Complete them to earn the full level reward (+10 XP, plus up to +10 XP for a perfect run). Progress is saved locally and shown on the Parent Dashboard.
Curriculum alignment
Mapped to national curriculum frameworks so teachers and parents can match practice to school standards.
- United StatesCommon Core State Standards for Mathematics · subtraction, place-valueAligned to subtraction, place-value number and operations objectives.
- United KingdomNational Curriculum for England — Maths · subtraction, place-valueAligned to subtraction, place-value number and operations objectives.
- AustraliaAustralian Curriculum v9.0 — Mathematics · subtraction, place-valueAligned to subtraction, place-value number and operations objectives.
- CanadaPan-Canadian Provincial Standards · subtraction, place-valueAligned to subtraction, place-value number and operations objectives.
Common questions from parents & teachers
Everything you need to know before your child starts playing.
- When the column you need to borrow from is empty, the borrow travels further left. Every zero it passes becomes a nine — so 305 is rewritten as 2 hundreds, 9 tens and 15 ones.
- Because children who learned borrowing as a fixed sequence try to take a ten from a column that has none, and either invent a nine or subtract the wrong way round.
- Because the cascade is what needs to be seen. Holding it in your head is exactly where it goes wrong.
- That game is the same method at two digits with a single exchange, for ages 5 to 7. This one adds the third column and the zero.
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