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Puzzle 1 of 6
A snail climbs 3 m by day and slides 2 m back at night. The well is 10 m deep. How many days to escape?
Correct. Not quite. Correct answer: 8
In the test, 609 people saw this puzzle and 16% got it right. The most common wrong answer was “10”, chosen by 51%.
The average-speed trap
The snail gains 1 metre per day, so 10 metres seems to take 10 days. But once it reaches the top, there is no night slide back.
On the morning of day 8 it is at 7 metres; that day it climbs 3 more and gets out. The answer is 8 days.
Answered on this page: 1
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Puzzle 2 of 6
What is the angle (in degrees) between the hour and minute hands at 3:15?
Correct. Not quite. Correct answer: 7.5°
In the test, 630 people saw this puzzle and 20% got it right. The most common wrong answer was “0°”, chosen by 42%.
The frozen hour hand
At 3:15 the minute hand points exactly at the 3, so the hands seem to overlap. But in those 15 minutes the hour hand has also moved a quarter of the way towards the 4.
Neighbouring numbers are 30° apart, and a quarter of that is 7.5°.
Answered on this page: 1
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Puzzle 3 of 6
Continue the sequence: 2, 3, 5, 7, 11, 13, ?
Correct. Not quite. Correct answer: 17
In the test, 829 people saw this puzzle and 24% got it right. The most common wrong answer was “15”, chosen by 52%.
It looks like odd numbers
3, 5, 7, 11, 13 is easy to read as the odd numbers, which would make 15 next. But the row starts with 2, and 9 is missing between 7 and 11.
These are prime numbers, divisible only by 1 and themselves. 15 divides by 3 and 5, so the next prime is 17.
Answered on this page: 1
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Puzzle 4 of 6
5ˣ = 25³. Find x.
Correct. Not quite. Correct answer: 6
In the test, 628 people saw this puzzle and 22% got it right. The most common wrong answer was “15”, chosen by 47%.
Multiplying instead of powers
The instinct is to multiply 5 by 3 and get 15. But 25 is 5², so 25³ = (5²)³.
When you raise a power to a power, you multiply the exponents: 2 × 3 = 6. That gives 5⁶, so x = 6.
Answered on this page: 1
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Puzzle 5 of 6
A lie detector is 95% accurate. 10% of people are liars. The test says someone is lying. Probability they actually are?
Correct. Not quite. Correct answer: ≈ 68%
In the test, 613 people saw this puzzle and 16% got it right. The most common wrong answer was “≈ 95%”, chosen by 36%.
Forgetting the base rate
Take 1,000 people. 100 of them are liars, and the detector catches 95. But it is also wrong about 5% of the 900 honest people, which flags another 45.
So 140 people get a “lying” result and only 95 of them really are: 95 / 140 ≈ 68%. A device's accuracy is not the chance that it is right about one particular person.
Answered on this page: 1
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Puzzle 6 of 6
On an island knights always tell truth, knaves always lie. A person says "I am a liar." Who is this person?
Correct. Not quite. Correct answer: Such a situation is logically impossible
In the test, 602 people saw this puzzle and 24% got it right. The most common wrong answer was “He is a knight”, chosen by 31%.
The liar paradox
A knight cannot say “I am a liar”: it would be a lie, and knights never lie. A knave cannot say it either: it would be true.
So nobody on the island can say this, and the situation is impossible. “Knight” and “knave” both look reasonable, but each contradicts the rules.
Answered on this page: 1
The full IQ test has 40 puzzles of different kinds. Taking it is free; the full result with your score and certificate unlocks with a one-time payment, no subscription.
How we counted
The figures come from answers in the IQMeter IQ test as of 2026-11-09: 3 696 completed tests and 147 902 answers. Automated runs (bots) are excluded. In the test, puzzles are solved against a timer, so the share of people who ran out of time is shown separately.
Participants are visitors to the site, mostly from Kazakhstan, Uzbekistan and Ukraine. They are not a sample of any country's population, so the figures describe how hard the puzzles are, not how smart people are.
Answers on this page are counted separately and do not enter the test statistics. You may reuse the data with a link to IQMeter (CC BY 4.0).