Cognilo
Mental math puzzles from everyday life
No flashcards and no stopwatch: these are the sums you actually meet in a shop, a restaurant or a train station. Work each one out in your head, then see the working and a faster technique for next time.
What is everyday mental math?
Everyday mental math means quick calculations with real quantities: money, time, percentages and unit prices. The numbers are rarely hard; the skill is choosing a simple route through them and keeping track of the intermediate result.
Each puzzle on this page is generated in your browser with clean numbers and four options. Three of the options are common slips, such as forgetting to subtract a discount or dividing before adding the tip, so a wrong answer usually tells you exactly which step went astray.
Five techniques that make mental arithmetic easier
Count up for change. To work out $10.00 minus $6.35, count up from $6.35: 65 cents reaches $7.00, then $3.00 reaches $10.00, so the change is $3.65. Counting up avoids borrowing.
Find 10% first. Moving the decimal point one place gives 10% of any price. Build other percentages from it: 5% is half of 10%, 25% is 10% + 10% + 5%, and 30% is three lots of 10%.
Jump to the hour. To add 38 minutes to 9:47, take 13 minutes to reach 10:00, then add the remaining 25 minutes: 10:25.
Compare like with like. To find the best value, convert every pack to the price per 100 g (or per item) before comparing. A bigger pack is often cheaper per gram, but not always.
Round, then adjust. $4.95 × 4 is $5 × 4 minus 4 × 5 cents: $20.00 − $0.20 = $19.80.
Answer to our coffee-break sum
Coffee $3.65 and a pastry $2.90, paid with a $10 note: the change is $3.45. The total is $6.55. Count up from $6.55: 45 cents reaches $7.00, then $3.00 reaches $10.00, so $3.45 with no borrowing.
Number puzzles in the Cognilo app
In the app, Real Numbers serves change, discount, bill-splitting, unit-price and timetable problems that step up as you clear levels. Market Run adds a short shopping list to remember, a budget and a substitution when an item is sold out. Every round ends with the working and a strategy tip, and both games are untimed in the default Precision mode.
Frequently asked questions
How can I practice mental arithmetic as an adult?
Use realistic problems, a few at a time, and always check the working afterwards. Learn one technique at a time, such as counting up for change or finding 10% first, and use it until it feels automatic. Short daily practice with feedback works better for most people than long, occasional sessions.
Are these mental math puzzles timed?
No. Nothing on this page is timed. In the Cognilo app, Precision mode is untimed and is the default; Sprint adds a clock only if you choose it.
Do I need to be good at maths to enjoy them?
No. The first levels use round numbers and one step. Difficulty in the app adapts to how you play, so the problems stay manageable while still giving you something to think about.