Brainteasers and puzzles for quant interviews

62 problems

Logic, number theory and geometry puzzles with one exact answer. Look for an invariant, a symmetry or a small case that exposes the pattern before you compute anything. Each problem has hints and a worked solution, free, no account.

#titlelevel
1 The blue-eyed islanders medium
3 Ants on a metre stick easy
4 A bee between two trains easy
5 Ten discs on three pegs easy
9 Cutting a cube into 27 easy
12 Splitting coins in the dark easy
15 The snail and the wall easy
20 A clock gone mad medium
22 One hundred hats in a line medium
25 A weighted geometric series easy
34 Walking down the escalator medium
37 Bricks in a box hard
38 One hundred in a circle medium
40 How often the hands meet easy
47 Digits that strictly increase easy
48 Four tyres and a spare easy
56 Chords between six points medium
57 The last digit of 17 to the 17th easy
60 Paths across a grid easy
62 One heavy coin in twenty-seven easy
63 An ant across a cube easy
67 A coin rolling around a coin easy
82 The Gaussian integral medium
84 Handshakes without crossing medium
85 Five sailors and the coconuts hard
115 A hole through a ball medium
116 How many coins in three weighings hard
118 Four people, one torch medium
123 Paying for the firewood easy
125 Lily pads with a head start easy
130 Positive eights, negative fives hard
133 Digit sums of a huge power hard
134 Twenty-five horses, five lanes medium
135 Two crossing pillars hard
142 Three daughters and a house number medium
149 Two eggs, one hundred floors medium
151 A clock with twin hands hard
153 Five pirates and a hundred coins medium
154 Average speed of a round trip easy
158 Rectangles on a chessboard easy
161 Drying potatoes easy
162 Six straight cuts easy
175 Four weights for forty pounds medium
186 x years old in the year x squared easy
198 Joining five chains medium
199 Two ferries medium
205 i to the power i easy
212 Change for a dollar medium
215 The angle at a quarter past three easy
216 One poisoned bottle in a thousand easy
219 A rope around the Earth easy
226 The camel and the bananas hard
228 Four gallons from a 3 and a 5 medium
233 Breaking a chocolate bar easy
242 How many ones easy
248 One hundred boxes hard
256 An infinite tower of powers medium
266 One hundred lockers easy
270 All the digits up to a million medium
271 Zeros at the end of 100! easy
272 Paint on a big cube easy
276 Digits adding to nineteen hard

Other topics: probability · random processes · order statistics · inference · regression · linear algebra · games · all problems