Yes. You can learn all 21 tricks as a guest without signing up, and there is nothing to buy. You only need a free PanicLines account if you want your progress on several devices.

How does the times 11 trick work?

For a two-digit number, split its digits apart and put their sum in the middle: 36 × 11 = 3 | 9 | 6 = 396. If the sum is 10 or more, carry the 1 to the first digit: 78 × 11 = 858.

Can I use SumFocus on my phone?

Yes. SumFocus is designed for phones and runs in the browser on smartphones, tablets and computers – nothing to download. You can even practise the learning path offline.

Is my progress saved?

Yes. As a guest it stays in this browser. With a PanicLines account it is saved on the server together with your streak and XP, so it is there on every device.

Mental Maths Tricks – Learn and Practise Online

Learn mental maths tricks online for free

SumFocus teaches you the shortcuts that make mental arithmetic fast: 48 × 5, 36 × 11, 35² or 15% of 240 become a couple of easy steps. Its 21 tricks sit on a learning path from easy to hard – from doubling and halving all the way to multiplying numbers just above 100.

You learn the way flashcards work: understand a trick, practise it with guidance, master it in a mini test, then review it at growing intervals so it sticks. It is built for phones but works just as well on a tablet or computer – free, and you can start as a guest without signing up.

How you learn a trick

Explanation: every trick starts with a short explanation and a fully worked example.
Guided practice: five tasks with hints. Each hint reveals one more step of the method.
Mini test: ten tasks that get gradually harder. Get at least 9 right and the trick is mastered, which unlocks the next one on the path.
Give a wrong answer and you immediately see the worked solution, step by step.

The 21 tricks

Times 5 · Times 4 and times 8 · Divided by 5 · Times 9 · Times 11 · Round & adjust · Times 15 · Times 25 · Divided by 25 · Complement to 1000 · Halve & double · Times 99 and times 101 · Squares ending in 5 · Split it · Percent · Divide by splitting · Ones make 10 · Squares near 50 · Close to 100 · Just above 100 · Around the middle (difference of two squares).

Reviews, XP and streaks

Mastered tricks move through six boxes, like a Leitner flashcard system. They come back for review after 1, 3, 7, 14, 30 and 60 days, and the tasks get harder with every box.
A review has four tasks per trick. Get three right and the trick moves up a box; otherwise it drops back to box 1 and returns tomorrow.
Each correct answer earns 10 XP, a newly mastered trick 50 XP and a passed review 20 XP. XP take you up the levels.
Learn every day to build a streak. Every 7 days you earn a streak freeze (up to two), which covers one missed day.

Controls

On a phone or tablet, tap your answer on the number pad and confirm with ✓; ⌫ deletes the last digit.
On a computer you can use the keyboard too: type the digits, Backspace deletes, Enter checks.

Mental maths tips

Go in order: the tricks build on each other. Once doubling and halving are second nature, times 4, times 25 and divided by 5 almost do themselves.
Say the steps quietly: "480, half of that, 240" – voicing the interim results keeps them from slipping away.
Estimate first: 48 × 52 is close to 50 × 50 = 2500. If your answer is far from that, something went wrong.
Don't skip reviews: a few minutes a day is enough. Spaced repetition is what makes a trick stay with you for good.
Use them in everyday life: work out discounts with the percent trick or tot up the shopping in your head – every real sum is extra practice.

Frequently asked questions

Is SumFocus free?: Yes. You can learn all 21 tricks as a guest without signing up, and there is nothing to buy. You only need a free PanicLines account if you want your progress on several devices.
How does the times 11 trick work?: For a two-digit number, split its digits apart and put their sum in the middle: 36 × 11 = 3 | 9 | 6 = 396. If the sum is 10 or more, carry the 1 to the first digit: 78 × 11 = 858.
Can I use SumFocus on my phone?: Yes. SumFocus is designed for phones and runs in the browser on smartphones, tablets and computers – nothing to download. You can even practise the learning path offline.
Is my progress saved?: Yes. As a guest it stays in this browser. With a PanicLines account it is saved on the server together with your streak and XP, so it is there on every device.