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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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12 problemsClear all filters

KA-0012
5 points, difficulty 3 of 3Level 3–4not yet calibrated
How many two-digit numbers have digits that add up to 8?
CNT-04Caseworkalso CNT-01, NUM-02
KA-0017
5 points, difficulty 3 of 3Level 3–4not yet calibrated
Ana says "Bo is lying." Bo says "Cal is lying." Cal says "Ana and Bo are both lying." How many of the three are telling the truth?
LOG-02Truth-tellers and liarsalso LOG-01, LOG-09
KA-0018
5 points, difficulty 3 of 3Level 3–4not yet calibrated
A three-digit code uses only the digits 1, 2 and 3, and digits may repeat. How many such codes contain at least one 3?
CNT-09Complementary countingalso CNT-03, CNT-04
KA-0020
5 points, difficulty 3 of 3Level 3–4has a figurenot yet calibrated
A square sheet is folded in half top to bottom, then in half left to right. One hole is punched through all the layers. How many holes are in the unfolded sheet?
GEO-15Paper folding and hole punchingalso GEO-08, GEO-09
KA-0133
5 points, difficulty 3 of 3Level 3–4not yet calibrated
How many squares of any size can be found on a 3 by 3 board?
CNT-13Counting shapes hidden inside a figurealso CNT-12, CNT-04
KA-0134
5 points, difficulty 3 of 3Level 3–4not yet calibrated
A square sheet is folded in half, then in half again. Two holes are punched through all the layers. How many holes are there when it is unfolded?
GEO-15Paper folding and hole punchingalso GEO-09, CNT-03
KA-0135
5 points, difficulty 3 of 3Level 3–4not yet calibrated
How many two-digit numbers have both of their digits odd?
NUM-02Digit-constraint puzzlesalso NUM-03, CNT-03
KA-0136
5 points, difficulty 3 of 3Level 3–4not yet calibrated
Four children stand in a line. Ana is not first. Bo stands directly behind Ana. Cal is last. Who is first?
LOG-04Ordering and ranking from cluesalso LOG-03, CFT-02
KA-0137
5 points, difficulty 3 of 3Level 3–4not yet calibrated
A jug holds 900 ml of juice. A third is poured out, then 150 ml is added. How many millilitres are in the jug?
MOD-10Multi-step arithmetic word problemsalso NUM-09, MOD-07
KA-0138
5 points, difficulty 3 of 3Level 3–4not yet calibrated
Squares of dots grow: 1 dot, then 4, then 9, then 16. How many dots are in the seventh square?
PAT-04Growth patterns and figurate numbersalso PAT-02, GEO-01
KA-0139
5 points, difficulty 3 of 3Level 3–4not yet calibrated
On a die, opposite faces add to 7. A die rests on a table with 3 on top. What do the four side faces add up to?
GEO-11Dice and cube face relationshipsalso NUM-08, CFT-05
KA-0140
5 points, difficulty 3 of 3Level 3–4not yet calibrated
A code uses the letters A, B and C, each exactly once. How many codes do not start with A?
CNT-03The multiplication principlealso CNT-11, CNT-09