Mental math tips
Mental math can be learned: a few simple techniques are enough to count faster and make fewer mistakes. Here they are, each with an example, then a tip for each game mode.
Keep a single total
Don’t memorize the series: keep a single number in mind, the total, and update it with each number that goes by. For 4, − 2, + 5, think “4”, then “2”, then “7”. Saying it under your breath helps not to lose it.
Go through ten
To add 7 to 8, first make 10: 8 + 2 = 10, 5 left, so 15. To subtract, the same the other way: 63 − 8 is 63 − 3 = 60, then − 5 = 55.
Spot the pairs
Two numbers in a row sometimes go together: 3 and 7, or 6 and 4, make 10; + 5 then − 5 cancel out. Add the pair in one go: one step less.
Left to right
With big numbers, add the tens first, then the units: 47 + 38 is 47 + 30 = 77, then + 8 = 85. The total stays right at each step, and you hold fewer digits at a time.
Round, then correct
A round number is easier to add: + 9 is + 10 − 1; − 98 is − 100 + 2. The correction is small, the sum much simpler.
By game mode
Each game mode has its traps. One tip for each, and the others on its page:
- Classic : Keep a single total in mind and update it with each number, rather than remembering the series.
- +1/−1 : Count the difference rather than the sum: a +1 and a −1 cancel out, only what's left counts.
- Multiplication : Apply each operation to the running result, in the order shown: 4, × 3, − 2 make 10, not −2.
- Intruder : The big number can come last: stay alert until the end.
- Decimals : Count in tenths: 2.5 − 0.8 is 25 − 8 = 17, so 1.7.
- Countdown : Add up what's taken away, then subtract it all at the end: 7 + 4 + 9 = 20, and 100 − 20 = 80.
- Percentages : Start from 10%: it's the number divided by 10. 5% is half of it, 20% twice it.
Practice
A few minutes a day beat a long session: one solo game is enough. After a mistake, look at the series, shown in full with the right total, to see where it slipped in. And when a mode gets easy, move on to another: each one trains something else.