About the mental math drill
The mental math drill trains arithmetic fluency: doing addition, subtraction, multiplication, and division in your head, quickly and accurately, under a clock. You choose which operations to practise, then answer a stream of problems whose difficulty rises with your score. It is built for students sharpening number sense, anyone preparing for timed aptitude tests, and people who simply want to stop reaching for a calculator to split a bill.
Speed in mental arithmetic is not about being "good at maths" innately; it is a trainable motor-and-recall skill. The big wins come from two places: automatic recall of the times tables and small sums, and a handful of decomposition tricks that turn an awkward problem into easy steps. Practising against a timer builds the recall, and seeing the same patterns repeatedly teaches the shortcuts. Everything runs in your browser and nothing you type is stored.
How it works
Under the hood the drill generates random operands, checks your typed answer instantly, and scales the number ranges as your score climbs. The mental techniques that make you fast are decompositions: breaking numbers into round chunks you already know.
add by rounding: 47 + 38 = (47 + 40) - 2 = 85 multiply by 11: 11 x 36 = 360 + 36 = 396 (or split the digits: 3_(3+6)_6) times 5: x5 = (x10) / 2, e.g. 48 x 5 = 480 / 2 = 240 percent: 18% of 50 = 50% of 18 = 9 (a% of b = b% of a) difficulty: operand range grows with score, so problems get harder
- Recall layer: the times tables to 12 and single-digit sums should be instant, with no counting.
- Decomposition layer: round to a friendly number, operate, then adjust back.
- Left-to-right: mentally it is easier to add the big digits first, the opposite of paper methods.
Worked example
The drill shows 7 x 48 and the clock is ticking. Rather than the paper algorithm, decompose it.
- Split 48: think of it as 50 minus 2.
- Multiply the round part: 7 x 50 = 350.
- Multiply the adjustment: 7 x 2 = 14.
- Subtract: 350 - 14 = 336.
Mental math techniques
| Operation | Trick | Example |
|---|---|---|
| Add near a round number | Round up, then subtract the excess | 68 + 27 = (68 + 30) - 3 = 95 |
| Subtract | Count up from the smaller number | 83 - 67: 67 to 83 is 16 |
| Multiply by 5 | Times 10, then halve | 34 x 5 = 340 / 2 = 170 |
| Multiply by 11 | Add the two digits between them | 11 x 45 = 4_(4+5)_5 = 495 |
| Multiply by 9 | Times 10, then subtract the number | 9 x 23 = 230 - 23 = 207 |
| Divide by 5 | Double it, then divide by 10 | 240 / 5 = 480 / 10 = 48 |
| Percentages | Swap the numbers (a% of b = b% of a) | 4% of 75 = 75% of 4 = 3 |
Common pitfalls
- Doing paper arithmetic in your head. The column-by-column, right-to-left method is slow mentally. Work left to right and round to friendly numbers instead.
- Weak times tables. If 7 x 8 is not instant, every multiplication built on it stalls. Drill the tables to 12 until they are pure recall.
- Holding too many digits at once. Mental working memory is small. Decompose into steps so you only ever juggle two or three numbers.
- Racing past accuracy. Speed without accuracy is worthless. Build correctness first; the speed follows the recall.
- Skipping estimation. A quick estimate (7 x 48 is "about 350") catches wild errors before you commit to an answer.
- Practising in long, tired sessions. Short, frequent drills build recall far better than occasional marathons, and fatigue tanks both speed and accuracy.
Related tools
Frequently asked questions
How can I get faster at mental math?
Two things: make the times tables and single-digit sums instant recall, and learn a few decomposition tricks like rounding to a friendly number then adjusting. Short, daily timed drills build the recall, and repeated exposure teaches the shortcuts.
Should I work left to right or right to left?
For mental math, left to right is usually easier. Adding the larger place values first gives you an early estimate and means you carry fewer digits in your head. The right-to-left column method is designed for paper, not for working memory.
What is the trick for multiplying by 11?
For a two-digit number, add its two digits and place the sum between them. For 11 x 45, add 4 and 5 to get 9, so the answer is 495. If the digit sum is 10 or more, carry the extra one into the left digit.
Does practising mental math make me smarter overall?
It reliably improves your arithmetic speed and number sense, which are useful everyday skills. Claims that it raises general intelligence are weakly supported; like most brain training, the clear gains are in the specific skill you practise rather than broad cognition.
Why do the problems get harder as I score?
The drill scales the size of the numbers with your score to keep you in the productive zone where you are challenged but still succeeding most of the time. That is where skill grows fastest; problems that are always trivial or always impossible teach little.