Here is another problem from the 2020 Math Calendar.
As a hint, recall that all the answers are integer days of the month. And the solution employs a technique familiar to these pages.
See Autumn Sum
Here is another problem from the 2020 Math Calendar.
As a hint, recall that all the answers are integer days of the month. And the solution employs a technique familiar to these pages.
See Autumn Sum
Again we have a puzzle from the Sherlock Holmes puzzle book by Dr. Watson (aka Tim Dedopulos). This one is quite a bit more challenging, at least for me.
“When Holmes and I met with Wiggins one afternoon, he was accompanied by a rather scrappy-looking mutt, who eyed me with evident suspicion.
‘This is Rufus,’ Wiggins said. ‘He’s a friend.’
‘Charmed,’ I said.
‘He’s very energetic,’ Wiggins told us. ‘Just this morning, he and I set out for a little walk.’
At the word ‘walk’, the dog barked happily.
‘When we set out, he immediately dashed off to the end of the road, then turned round and bounded back to me. He did this four times in total, in fact. After that, he settled down to match my speed, and we walked the remaining 81 feet to the end of the road at my pace. But it seems to me that if I tell you the distance from where we started to the end of the road, which is 625 feet, and that I was walking at four miles an hour, you ought to be able to work out how fast Rufus goes when he’s running.’
‘Indeed we should,’ said Holmes, and turned to look at me expectantly.
What’s the dog’s running speed?”
See the Rufus Puzzle
This is another delightful Brainteaser from the Quantum math magazine.
“All the vertices of a polygonal line ABCDE lie on a circumference (see the figure), and the angles at the vertices B, C, and D are each 45°.
Prove that the area of the blue part of the circle is equal to the area of the yellow part. (V. Proizvolov)”
I especially liked this problem since I was able to find a solution different from the one given by Quantum. Who knows how many other variations there might be.
See the Circle-Halving Zigzag Problem
This is a simple logic puzzle from one of Ian Stewart’s many math collections.
Therefore:
Elephants are easy to swallow.
Is the deduction correct, or not?
In my search for problems I decided to purchase Dan Griller’s GCSE problem book mentioned in the Cube Roots Problem. I am still a bit confused about the purpose of the GCSE exam and who it is for, since the other problems in Griller’s book are often as challenging or more so than the cube roots problem. It is hard to believe students not pursuing college level degrees could solve these problems. (Grades 8 and 9 referred to in the subtitle of the book must indicate something other than US grades 8 and 9, since the exams are aimed at 16 year-olds, not 13 and 14 year-olds.)
Supposedly the problems in Griller’s book are nominally arranged in increasing order of difficulty from problem 1 to problem 75. However it seemed to me that there were challenging problems scattered throughout and the last problem was not all that much harder than earlier ones. And many of them had a whiff of Coffin Problems—they seemed impossible at first (Problem 44: Construct a 67.5° angle!). I don’t know how many problems are on the exam or how long the exam is, but anyone taking a timed exam does not have the leisure to mull over a problem. The student only has a few minutes to come up with an approach and clever insights are rare under the circumstances. Anyway, here is the last problem in the book.
“Problem 75. A square pond of side length 2 metres is to be surrounded by twelve square paving stones of side length 1 metre.
(a) The first design is constructed with a circle whose centre coincides with the centre of the pond. Calculate exactly the total dark grey area for this design.
(b) The second design is similar. Calculate exactly the total dark grey area for this second design.”
See the Pool Paving Problem
Here is a nice logic puzzle from 2014 Futility Closet.
“Only one of these statements is true. Which is it?
_________A. All of the below
_________B. None of the below
_________C. One of the above
_________D. All of the above
_________E. None of the above
_________F. None of the above”
See Pointing Fingers.
For a change of pace, here is an early puzzle from Alex Bellos in The Guardian.
“Happy New Year guzzlers! Today’s first problem concerns squirrels. Have a nibble—it’s not too hard a nut to crack.
The Squirrel King has buried the Golden Acorn beneath one of the squares in this 6x6 grid. Three squirrels—Black, Grey and Red—are each standing on a square in the grid, as illustrated.
(Note: for the purposes of today, squirrels can speak, hear, read, count and are perfect logicians. They can also move in any direction horizontally and vertically, not just the direction these cartoons are facing. They all can see where each other is standing, and the cells in the grid are to be considered squares.)
The Squirrel King hands each squirrel a card, on which a number is written. The squirrels can read only the number on their own card. The King tells them: ‘Each card has a different number on it, and your card tells you the number of steps you are from the square with the Golden Acorn. Moving one square horizontally or vertically along the grid counts as a single step.’ (So if the acorn was under Black, Black’s card would say 0, Grey’s would say 4, and Red’s 5. Also, the number of steps given means the shortest possible number of steps from each squirrel to the acorn.)
The King asks them: ‘Do you know the square where the Golden Acorn is buried?’ They all reply ‘no!’ at once.
Red then says: ‘Now I know!’
Where is the Golden Acorn buried? …”
See the Squirrel Puzzle
Yet another interesting problem from Presh Talwalkar.
“Two side-by-side squares are inscribed in a semicircle. If the semicircle has a radius of 10, can you solve for the total area of the two squares? If no, demonstrate why not. If yes, calculate the answer.”
This puzzle shares the characteristics of all good problems where the information provided seems insufficient.
See the Sum of Squares Puzzle.
Here is a collection of puzzles from the great logic puzzle master Raymond Smullyan in a “Brain Bogglers” column for the 1996 Discover magazine.
See Family Values.
This is a problem from the UKMT Senior Challenge for 2019. (It has been slightly edited to reflect the colors I added to the diagram.)
“The edge-length of the solid cube shown is 2. A single plane cut goes through the points Y, T, V and W which are midpoints of the edges of the cube, as shown.
What is the area of the cross-section?
A_√3_____B_3√3_____C_6_____D_6√3_____E_8”