Mental math
Break calculations into parts, use multiplication shortcuts, and reconstruct missing numbers.
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Your path
Read the method, then put it to work.
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Calculate in useful parts
Split a number, calculate each part, then combine the results.
Lessons & practices
LessonMultiply in parts 3 min readPracticeStart with Calculate. When ready, choose Multi-step for expressions and word problems using fractions, percentages, and decimals. Every answer is a whole number.
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Use multiplication shortcuts
Recognize a useful number pattern before carrying out the multiplication.
Lessons & practices
LessonMultiplication shortcuts 3 min readPracticeThe lesson introduces Classic methods. Choose Extended when ready for matching tens with units that add to 10, and numbers above or below 100 and 1,000.
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Reconstruct a number
Combine clues about digits and number properties, then verify the complete answer.
Lessons & practices
LessonReconstruct from number clues 4 min readPracticeUse the lesson to combine digit and number clues, then check every condition. Practice opens Extended Level 1 and is currently in English.
Go further
Try a harder setting, apply the method in another practice, then review what changed.
Optional practice. Your rounds appear in Progress; your completed modules stay complete.
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Keep track of linked calculations
Open Multi-step at Medium. Extend the lesson’s splitting method to brackets, fractions and linked story steps. Find each useful subtotal before combining the parts.
Lessons & practices
LessonPracticeAfter your round
For a missed answer, locate the first incorrect operation in the worked method. Recalculate from that point and check the operation order. For a story problem, also check the final units. -
Multiply around a shared base
Open Extended, Level 2, Ten questions. Apply the lesson’s signed offsets to two numbers above 100: add both offsets to the base, multiply by 100, then add the product of the offsets.
Lessons & practices
LessonPracticeAfter your round
Explain one answer using both splitting and offsets. Then try Level 3: with one number below 100, explain why the offset product must be subtracted. -
Reconstruct from several clues
After the reconstruction lesson, open Extended at Level 2. Number Challenges is in English. Combine every digit constraint, narrow the possible roots, and complete missing digits in squares and cubes.
Lessons & practices
PracticeAfter your round
Check a reconstructed number against every clue. For a missing power, square or cube the proposed root to verify all visible and missing digits, then explain why your first candidate failed.