From checking divisibility without doing the division to quickly calculating multiplication, division, and percentages mentally, plus common mistakes made on tests — these are practical tips you can use right away. Click a card to explore each one.
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Divisibility Rules
Check whether a number is divisible by another number just by looking at its digits, without doing the division itself.
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Mental Multiplication Tricks
Learn quick ways to calculate 11 times a number, 5 times a number, and the square of a two-digit number mentally without a calculator.
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Mental Division Tricks
Turn division by 5 and division by 25 into multiplication to make mental calculations much easier.
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Mental Percentage Tricks
Once you know 10%, 5%, and 1%, you can mentally calculate any percentage by combining them.
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Square Root Estimation Tricks
Estimate square roots quickly between nearby perfect squares, even without a calculator.
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Fraction–Decimal Conversion Memory Tricks
Learn to memorize commonly used fraction–decimal pairs efficiently by grouping them into families.
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Fraction Comparison Shortcuts
Compare fractions quickly with one cross-multiplication, without finding a common denominator.
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Memorizing Powers of Two
Learn an efficient way to memorize frequently used powers of 2: 2, 4, 8, 16, 32, and so on.
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Exam Mistake Checklist
Review common exam mistakes such as dropping signs, failing to simplify fractions, or leaving out units, along with ways to prevent them.
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Distance–Speed–Time Formula Triangle
Remember one triangle and you can immediately tell whether to multiply or divide when finding distance, speed, or time.
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Celsius–Fahrenheit Temperature Conversion
Remember F = 1.8×C + 32 and you can quickly estimate Fahrenheit temperatures from Celsius.
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