Everyday Mental Math
Ditch the calculator app and build instant number confidence. Learn simple mental tricks to calculate tips, spot real discounts, and estimate anything on the fly.
Like Duolingo, but for Everyday Mental Math. Tomo turns the whole topic into a game you play five minutes a day, until it actually sticks.
A short one: 12 levels across 2 sections, about 24 minutes end to end, roughly 5 days at five minutes a day. It moves through Instant Calculations in Your Head and Sanity-Checking the Real World. It starts from scratch.
Free forever · No credit card · iPhone & Android
Key ideas in Everyday Mental Math
- Everyday percentages can be constructed by adding or subtracting easy anchor amounts like 10%, 5%, and 1%
- Breaking a percentage down eliminates the need to multiply by multi-digit decimals
- 10% represents one tenth of an amount, which mathematically shifts every digit one place value to the right
- Practically, moving the decimal point one spot to the left gives 10% immediately without performing long division
- 5% is exactly half of 10%, so you halve your 10% answer
- 20% is exactly twice 10%, so you double your 10% answer
- Percentages are reversible because multiplication is commutative: x% of y equals (x × y) ÷ 100, which equals y% of x
- Swapping the numbers lets you replace a tricky percentage like 18% with an easy one like 50% (half of 18 is 9)
- Real-world tips can be calculated in two steps: find the easy anchor values first, then add them together
- Finding 10% and single percentages (1%) provides the components needed to form figures like 18%
- Adding the largest place value first lets you update a single running total in your head
- Mental addition avoids the need to juggle and store carried digits across columns
- Splitting the second number into tens and units simplifies the sequence
- Subtracting an easy round number like 30 is much faster than subtracting 29
- Because subtracting 30 removes 1 too many, you restore balance by adding 1 back at the end
- Halving one factor while doubling the other leaves the total product unchanged
You've tried the other tabs
Thirty open tabs. Four facts you actually kept.
You watched. You nodded. By Sunday it was gone.
One answer, then back to scrolling.
Eight weeks. You meant to finish. You didn't.
Tomo gives Everyday Mental Math the Duolingo treatment: levels, streaks, and quick quizzes that test what you just learned. That game loop is what the tabs above never had, so it's the one you actually finish.
Here's what playing it feels like
A real question from this course. Take your best guess.
Why is it helpful to break a percentage down into smaller friendly pieces?
Get it right to open this lesson and 11 more in the app.
Where Everyday Mental Math takes you
- 1
Instant Calculations in Your Head
- Benchmark Percentages
- Mental Arithmetic Shortcuts
- 2
Sanity-Checking the Real World
- Back-of-the-Envelope Estimation
- Comparing Real-World Value
2 sections · 4 units · 12 levels. Built to play, not to enroll.
Tomo is in ChatGPT
Tomo is also a ChatGPT plugin: the same playable courses, built and played inside your chat.
Add Tomo to ChatGPT- What to ask
- “Make me a Tomo course on black holes.” “Turn this chat into a Tomo course.”
- What you get
- Quick questions with instant feedback, hearts and stars, ready to play in about a minute.
- Where it goes
- No sign-up to start. Connect your Tomo account and your streak carries on in the app.
You pick the voice
Everyday Mental Math is taught in the Bestie style: your friend who just gets it. Want a different feel? In the app you can spin up the same topic in any of Tomo's teaching styles. Same facts, totally different vibe.
More Math on Tomo
Mental Math for Everyday Life
Ditch the phone calculator and build intuitive number sense. Learn the mental shortcuts that turn everyday tips, discounts, and ballpark calculations into second nature.
Everyday Mental Math
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Applied Mental Arithmetic
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ASVAB Core Skills
Build the math and language confidence needed to conquer the ASVAB. Master fractions, word context, and arithmetic reasoning while unlocking the strategies that maximize your AFQT score.
Mastering 5th Grade Math
Stop feeling stuck and start solving problems like a pro. Learn the tricks to handle big numbers and shapes so you can tackle real-world challenges with confidence.
Start Everyday Mental Math today.
Download Tomo, search Everyday Mental Math, and play your first lesson in under a minute.