Fill the Missing Part
Complete number bonds by finding the missing part — 7 = 3 + ?. Visual circles and connecting lines show the whole and its parts. Race the clock in 60-second mode or survive on 3 lives. Easy, medium, and hard levels.
More like this
How to Play Number Bond Builder
Choose Difficulty and Mode
Pick Easy (bonds to 10), Medium (to 20), or Hard (to 50). Then select 60-Second Rush or Survival (3 lives).
Look at the Bond Diagram
A top circle (the whole) is connected by lines to two bottom circles (the parts). One of the three circles is missing — it shows a pulsing '?' mark.
Tap the Correct Answer
Four buttons offer possible answers. Figure out the missing number: if you see 9 = ? + 4, the answer is 5. Tap the matching button or press 1–4 on desktop.
Build Your Streak
Correct answers build a fire streak. In Rush mode, keep solving until the 60 seconds are up. In Survival, avoid 3 mistakes to stay alive.
Key Features
Visual Number Bond Diagram
A beautiful circle-and-line diagram shows the whole number at top connected to two parts below — the classic number bond shape children learn in school. The missing part pulses to draw attention.
Three Difficulty Levels
Easy uses bonds up to 10, with only parts missing. Medium raises the ceiling to 20 and sometimes hides the whole. Hard goes up to 50 and any position can be missing — great for developing flexible addition and subtraction thinking.
60-Second Rush and Survival Modes
In Rush mode, solve as many bonds as you can before time runs out. In Survival mode, you have 3 lives — each wrong answer costs one. Same bonds, completely different pressure.
Four Colorful Multiple-Choice Buttons
Big indigo, rose, amber, and teal buttons make answering easy on touch screens. Keyboard shortcuts 1–4 enable fast desktop play. Correct answers flash green; mistakes turn red and reveal the answer.
What is Number Bond Builder?
Number Bond Builder is a fast-paced math game that challenges players to complete number bonds — a visual representation of how a number splits into two parts. A circle-and-line diagram shows the whole at the top connected to two parts at the bottom, and one of the three values is hidden. Players choose the correct missing number from four colorful choices. Easy mode keeps bonds within 10 (perfect for learning addition facts), Medium extends to 20 and sometimes hides the whole, and Hard goes up to 50 with any part potentially missing. The game reinforces the fundamental relationship whole = part + part, which underpins addition, subtraction, and algebraic thinking.
Why Play Number Bond Builder?
Builds Part-Whole Understanding
Number bonds teach children that every addition fact is also a subtraction fact. Seeing 8 = 3 + 5 means you also know 8 − 3 = 5 and 8 − 5 = 3 — one diagram, three facts.
Develops Mental Math Fluency
Rapid recall of bonds to 10 and 20 is the foundation of multi-digit arithmetic. Practicing until bonds become automatic frees working memory for harder problems.
Visual Learning Advantage
The circle-and-line diagram is used worldwide in Singapore Math and other curricula. Playing with the same visual at speed reinforces classroom learning.
Prepares for Algebra
Filling in the missing part of a + b = c is the same structure as solving a simple equation. Early exposure through bonds builds confidence with variables later.
Frequently Asked Questions
What is a number bond?
A number bond is a visual showing how one number (the whole) breaks into two parts that add up to it. For example, 10 = 6 + 4. It's typically drawn as three circles connected by lines — the whole on top and the two parts on the bottom.
Which part can be missing?
On Easy mode only one of the two parts is missing (e.g., 7 = 3 + ?). On Medium and Hard the whole can also be missing (e.g., ? = 5 + 8), requiring players to add rather than subtract.
What age is this game for?
Easy mode (bonds to 10) suits ages 5–7 who are learning basic addition facts. Medium (to 20) fits ages 7–9. Hard (to 50) challenges older students and adults who want to sharpen mental math.
Can I use keyboard shortcuts?
Yes! Press 1, 2, 3, or 4 to select the corresponding colored button. This lets desktop players answer quickly without reaching for the mouse.
Are scores saved?
Yes. Your best score is saved locally in your browser for each combination of difficulty and game mode. It's shown on the settings screen so you always know what to beat.