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Mental math tricks
Need a mental math tricks within reach? Print it for the wall, then hand off to the practice sheets below.
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Reference chart
Mental math tricks
Pairs that make a round number
- 25 × 4100a quarter of a hundred, four times
- 125 × 81,000an eighth of a thousand, eight times
- 50 × 2100half of a hundred, twice
- 20 × 5100and 2 × 5 = 10, ten times over
Swap the hard number for an easy one
- 18 × 590× 10, then halve: 180 ÷ 2
- 7 × 963× 10, then take one off: 70 − 7
- 23 × 492double, then double again: 46 → 92
- 340 ÷ 568× 2, then ÷ 10: 680 ÷ 10
Patterns worth spotting
- 25 × 36900rearrange to the round pair: 25 × 4 × 9
- 35 × 351,2253 × 4 = 12, then 25 on the end
- 24 × 11264outside digits, middle is 2 + 4
- 13 × 991,287× 100, then one lot off: 1,300 − 13
What's on this chart
These are not tricks in the sense of being arbitrary. Every one is a fact about how our number system is built, and that is why the chart prints the reason next to the shortcut rather than the shortcut alone. A child who memorises 25 × 4 = 100 has one fact; a child who knows it because a quarter of a hundred is 25 also has 25 × 8, 25 × 12, and the confidence to try 25 × 36.
Why this chart helps
That last one is the real payoff, and it is the first group's whole purpose. 25 × 36 looks like a written-method problem. Rearranged as 25 × 4 × 9 it is 100 × 9, which is 900, and it is done in one step in your head. Spotting a round pair hiding inside an awkward multiplication is the single most useful habit on this page.
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