Everyday Mental Math
Ditch the calculator and build effortless numerical intuition for real life. Learn how to mentally calculate tips, spot misleading discounts, estimate big numbers in seconds, and make smarter decisions with odds and percentages.
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 Calculating in Your Head and Decoding Proportions and Odds. It starts from scratch.
Free forever · No credit card · iPhone & Android
Key ideas in Everyday Mental Math
- Finding 10% of any number requires shifting the decimal point one place to the left
- A 15% tip is simply 10% plus half of that 10% (5%)
- Halving $6.40 gives $3.20, and adding $6.40 + $3.20 gives $9.60
- Percentages can be swapped because x% of y is mathematically identical to y% of x (x * y / 100 = y * x / 100)
- Swapping makes mental calculation instant whenever one of the numbers is a friendly benchmark like 50, 25, or 10
- If an item is discounted by a certain percentage, you pay the remaining percentage that adds up to 100%
- A 25% discount means you pay 75% (or 3/4) of the original price
- Multiplying directly by the remaining percentage avoids the two-step process of calculating the discount and subtracting it
- Dividing odd totals like $93.40 by 4 leads to messy decimals that complicate splitting
- Rounding the grand total up to a multiple of the headcount (like $96 or $100) makes mental division immediate
- Small rounding surpluses can easily cover extra tip or be balanced with pocket change after division
- Awkward percentages can be split into sums or differences of familiar landmarks (50%, 25%, 10%, 5%, 1%)
- 1% is found by moving the decimal two places left; 10% by moving it one place left
- Subtracting 1% from 20% or 5% from 50% is faster than building up from scratch
- Rounding numbers to their nearest power-of-ten friendly values (like 50 and 200) gives the rough scale of the answer immediately
- Order-of-magnitude estimation checks whether the result is in the thousands, tens of thousands, or hundreds, catching misplaced decimals or typos without exact math
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.
What is the quickest way to find 10% of your bill in your head?
Get it right to open this lesson and 11 more in the app.
How to learn Everyday Mental Math, step by step
Go in order. 12 short levels across 2 sections, about 24 minutes in all, five minutes a day.
- 1
Calculating in Your Head
- Everyday Shortcuts for Tips and Discounts
- Fast Ballpark Estimation
- 2
Decoding Proportions and Odds
- Making Sense of Percentages and Rates
- Intuitive Probability and Risk
2 sections · 4 units · 12 levels. Built to play, not to enroll.
Questions about Everyday Mental Math
How do I learn Everyday Mental Math?
Go in order: start with Calculating in Your Head, then Decoding Proportions and Odds. On Tomo that's 12 short levels, about 24 minutes in all, played five minutes a day. Start free and play the first level in under a minute.
Is there a Duolingo-style app for Everyday Mental Math?
Yes. Tomo works like Duolingo: short daily lessons, streaks and quick quizzes. Everyday Mental Math is one of its free courses, and you can type any other topic to get a course of your own.
Is the Everyday Mental Math course free?
Yes. Everyday Mental Math is playable on Tomo's free plan, which doesn't expire. No credit card, no waitlist. Download the app and start your first lesson.
How long does it take to learn Everyday Mental Math?
12 levels across 2 sections, about 24 minutes of play in total. It's built for five minutes a day, so you finish it a little at a time instead of all at once.
Do I need any background to start Everyday Mental Math?
No. It's pitched at a beginner level, so it starts where you are and builds up. If you can tap a phone, you can start.
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
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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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Spotting Misleading Numbers
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Canadian Lynx Math Contest Strategies
Unlock competition math techniques used in the Canadian Lynx Mathematical Contest. Master high-yield problem patterns in algebra, geometry, number theory, and combinatorics to solve complex questions with speed and precision.
Start Everyday Mental Math today.
Download Tomo, search Everyday Mental Math, and play your first lesson in under a minute.