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20
5
Odd Pills
Your pharmacist gives you 5 jars filled with pills. The pills contained in each jar have an identical appearance and size (i.e. if you mixed all of the pills you wouldn't be able to tell them apart).
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Doable
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15
25
Multiples of 8 plus 1
Squaring the first several odd numbers reveals the following pattern:
3 squared = 8 + 1
5 squared = 24 + 1
7 squared = 48 + 1
8, 24, and 48 are all multiples of 8. Does this pattern hold for all squa
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Doable
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15
12
Swap Variables in Place without XOR
Suppose you have two variables, a and b. How can you swap their values without using a temporary variable and also without using the bitwise operator XOR?
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Doable
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14
7
Coin Flip
On Monday, you flip a coin all day. You start flipping it until you see the pattern Head, Tail, Head. You record the number of flips required to reach this pattern, and start flipping again (and co
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Doable
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12
6
The double-square number problem
It's said that a number N with 4 digits is a double-square number when it equals the sum of the squares of two numbers: one formed by the first two digits of N, in the order they appear in N and the ot
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Hard
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10
16
3 Coins
Not sure what the answer is, ideas welcome!
You have 3 coins, one always comes up heads, the second always comes up tails, and the third is a fair coin. You select a coin at random. After selecting
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Easy
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10
2
Two Trains
Two trains (Train A and B) with 200 km between them are travelling towards each other at 100km/h. A mosquito, initially standing on the front of Train A, starts travelling towards Train B at 150km/h. O
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Doable
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9
9
1978
The year 1978 is such that the sum of the first two digits and the latter two digits is equal to the middle two digits, i.e. 19 + 78 = 97. What is the next year (after 1978) for which this is true?
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Doable
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8
8
The Famous Hole in a Sphere
This incredible problem was first made famous by Martin Gardner with his ‘Mathematical Games’ column published in Scientific American throughout the 60s and 70s.
A cylindrical hole, 6 inches long,
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Hard
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7
9
Non-Adaptive 12 Identical Balls
Okay - so I posted this puzzle to reddit a few weeks ago and one guy had the following comment:
Same problem, but your solution must be non-adaptive. IOW, specify the weighings that you will make up f
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Hard
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7
3
Tea and Wine
You take a spoon of wine from a barrel of wine and put it into your cup of tea. Then you return a spoon of the (non-uniform) mixture of tea and wine from your cup and put it in the barrel. Now you ha
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Doable
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