Every door shows you the result and hides the starting number, work backwards with inverse operations and crack it before the charge runs out.
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How to play
Each door displays an equation with the answer already given and the input missing. Reverse the operations, undo a plus with a minus, a times with a divide, to recover the value that makes it true, then key it in. Every door starts with a full charge that ticks down, so solve and enter before it empties. Clear the run of doors to finish.
The result is shown; you supply the hidden input.
Apply inverse operations to peel the equation back.
Each door's charge bar depletes, answer before it runs dry.
A run is a set sequence of doors at your chosen difficulty.
Game modes
Daily (seeded): the same run for everyone, in Easy, Medium, or Hard.
Practice (random): fresh runs at your chosen difficulty.
Controls
Desktop: type your answer on the on-screen keypad and confirm.
Phone & tablet: tap the number keypad to enter the missing value.
Tips & strategy
Read the equation right-to-left: the last operation applied is the first one you undo.
Estimate the input's rough size first so you can type confidently before the charge fades.
On harder doors, undo one step at a time rather than trying to solve it all in your head.
What you'll learn
Boost Code drills inverse operations by flipping the usual problem, you are handed the answer and must rebuild the steps that reach it.
Skills: inverse operations, working backwards, the four operations, algebraic thinking
Best for: roughly grades 4–7 (ages 9–13)
For parents & teachers: builds the 'undo' thinking that later powers equation-solving.
About Boost Code
Boost Code is an original, free browser math game that drills inverse operations by flipping the usual problem, you're handed the answer and must rebuild the question. No sign-up needed.
A free, original browser game on PlayPendium. No download, no install.
