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The whole Atlas

Number & Arithmetic15
Counting18
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Logic & Deduction11
Patterns & Sequences7
Modeling & Word Problems10
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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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19 problemsClear all filters

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-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
KA-0157
5 points, difficulty 3 of 3Level 7–8not yet calibrated
A drawer holds 12 red socks, 10 blue socks and 8 green socks, all mixed up. You take socks out one at a time in the dark. What is the smallest number of socks you must take to be certain of having three of the same colour?
CNT-17The pigeonhole principlealso CNT-18, LOG-09
KA-0166
5 points, difficulty 3 of 3Level 9–10not yet calibrated
Six friends sit around a circular table. Two seatings count as the same if one can be turned into the other by rotating the table. How many genuinely different seatings are there?
CNT-15Counting up to symmetryalso CNT-16, CNT-05
KA-0168
5 points, difficulty 3 of 3Level 9–10not yet calibrated
An ordinary six-sided die is rolled three times. What is the probability that at least one roll shows a six?
CNT-09Complementary countingalso CNT-16, CFT-11
KA-0175
5 points, difficulty 3 of 3Level 11–12not yet calibrated
What is the smallest number n such that ANY collection of n whole numbers must contain two of them whose difference is divisible by 7?
CNT-17The pigeonhole principlealso NUM-06, LOG-09
KA-0177
5 points, difficulty 3 of 3Level 11–12not yet calibrated
How many diagonals does a convex polygon with 12 sides have? A diagonal joins two vertices that are not already joined by a side.
CNT-16Overcount, then correctalso CNT-06, GEO-05

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