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Number & Arithmetic15
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177 problems, every one written from scratch, every wrong answer carrying the mistake that produces it. 708 explanations in all.

Level

1–2
3–4
5–6
7–8
9–10
11–12

Point value

3 pt
4 pt
5 pt

Strand

NUMNumber & Arithmetic
CNTCounting
GEOGeometry & Visualization
LOGLogic & Deduction
PATPatterns & Sequences
MODModeling & Word Problems
CFTContest Craft

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8 problemsClear all filters

KA-0007
4 points, difficulty 2 of 3Level 3–4not yet calibrated
Nadia gave half her stickers to her brother, then 6 more to a friend. She has 9 left. How many stickers did she start with?
LOG-08Working backwardsalso NUM-09
KA-0091
4 points, difficulty 2 of 3Level 3–4not yet calibrated
Ana, Bo and Cal each keep a different pet: a cat, a dog and a fish. Ana does not keep the cat. Bo keeps neither the cat nor the fish. Who keeps the cat?
LOG-03Elimination gridsalso LOG-01
KA-0092
4 points, difficulty 2 of 3Level 5–6not yet calibrated
Five children queue up. Ana is somewhere ahead of Bo. Cal is behind Bo but ahead of Dee. Eve is last. Who is second in the queue?
LOG-04Ordering and ranking from cluesalso LOG-01, CFT-02
KA-0093
4 points, difficulty 2 of 3Level 3–4not yet calibrated
Two apples balance three pears. One apple weighs 90 grams. How many grams does one pear weigh?
LOG-10Weighing and balance puzzlesalso NUM-11, MOD-01
KA-0096
4 points, difficulty 2 of 3Level 3–4not yet calibrated
Ana says: "Bo and I are both liars." Each child is either always truthful or always a liar. Who is telling the truth?
LOG-02Truth-tellers and liarsalso LOG-09, LOG-01
KA-0099
4 points, difficulty 2 of 3Level 3–4not yet calibrated
All the red boxes are heavy. Box X is not heavy. What must be true?
LOG-01Reading a logical statement preciselyalso LOG-09
KA-0100
4 points, difficulty 2 of 3Level 5–6not yet calibrated
A number is doubled, then 6 is added, then the result is halved. The answer is 11. What was the original number?
LOG-08Working backwardsalso MOD-01
KA-0102
4 points, difficulty 2 of 3Level 3–4not yet calibrated
Cards numbered 1 to 10 lie face up. You take any six of them. Must two of your cards add up to 11?
LOG-09Informal proof by contradictionalso CNT-17, NUM-03

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