Alice and the pies

October 1, 2021Arithmetic, Lewis CarrollTeun Spaans

Alice and the March Hare had a Christmas lunch. Alice had baked 5 pies, the March Hare 3.
“It’s tea time,” the March Hare said. “So let’s eat the pies.”. The Mad Hatter popped in.
“It’s lunch time, not tea time,” Alice said. “But we can eat the pies.”
Each pie was cut into 3 parts, with one part eaten by each of the three.
“It was the best butter, you know” the March Hare said. “And there’s nothing better than the best butter, you can’t deny that.”
Alice looked surprised at him, as she didn’t understand why he made that remark.
“Well, I think they all are delicious”

At the end, the Mad Hatter thanked them, paid 8 pounds and left.

“Now that’s 5 pound for you and 3 for me,” the March Hare said.
But Alice doubted this was fair. Was Alice right?

I found this problem at https://plus.maths.org/content/sharing-cakes. Reportedly, a version of it was written by Ali ibn Abi Talib in the seventh century AD. Another version appears in Fibonacci’s famous Liber Abaci.

New puzzles are published at least twice a month on Fridays. You can check your solution here.

18 matchsticks aka 18 nails aka 18 toothpicks

September 17, 2021MatchsticksTeun Spaans

It’s a while ago we had matchstick puzzles, so here’s one again. And yes, you are perfectly right, matches are on the way out with electric cooking and all such. Luckily, you can use nails or toothpick sticks instead. I mentioned it in a previous post and I’m now also mentioning it in the title of the post.

In the image below you see 18 matchsticks aka nails aka toothpicks making up six squares. Now re-arrange the 18 matchsticks to make twenty.

New puzzles are published at least twice a month on Fridays. You can check your solution here.

The successor of the sultan (4)

September 3, 2021Deduction, Logic, UncategorizedTeun Spaans

The sultan asked the vizier:
“The tests so far for finding my successor are way too easy. We’ve got to make them harder. There are still dozens of candidates left.”
“This one is definitely more difficult. First, they got to swim”
“So they had in the previous test,” the sultan grumbled.
“If they come up to breath, there heads will be shot off,” the vizier explained. The sultan nodded approval.
“There are four doors.”
“So had the previous test”
“But now there are two labels on every door. So they’ve got to think twice as fast!”

Test 4^***/*****

The first candidate look at the four doors.
“Again only one door hides a treasure,” the vizier explained. “There is a shark behind each of the other three.”
The candidate looked at the labels. He could see that there were two labels on each door, but he couldn’t read them.
“And how many labels are true? Or how many doors have true labels?”
“That is a very good question”, the sultan smiled. “As a matter of fact, knowing which door hides the treasure, it was impossible to decide upon the number of true labels. So how you should decide the number of true labels while you don’t know which door hides the treasure, is beyond me.”

Which door should the candidate open?

New puzzles are published at least once a month on Fridays. Solutions are published after one or more weeks. You are welcome to remark on the difficulty level of the puzzles, discuss alternate solutions, and so on. Puzzles are rated on a scale of 1 to 5 stars. You can check your solution here.

The numbers 1 – 9 and combinatorics.

August 20, 2021CombinatoricsTeun Spaans

As children, we all learned to count. Thus we rarely think about counting as ‘difficult’. Yet mathematicians have developed a special branch of mathematics for the art of counting. The branch is called Combinatorics. Typical questions in Combinatorics are:
1) In how many ways can a stack of 52 playing cards be arranged?
2) When we have a vase with 5 black and 5 white balls, in how many sequences can we pull them out?

In today’s problems, we work with the cards 1 to 9:

1) How many ways?^*/*****
It is easy to arrange these cards into 3 groups, all with the same sum:

One reason it is easy, is because there are several solutions. Withe sum of the 9 cards being 45, each of the three groups will have to have sum 15. But in how many ways exactly can we divide the cards 1-9 into three groups, all with the same sum?

2) Be creative^****/*****
Now be creative in the arrangement of your cards. In how many ways can you create 3 groups in such a way that the three groups still all have the same sum, but the sum is not 15?
Yeah, you may cheat in this problem. But your cheating is limited to arranging the cards.

3) Combinatorics (unsolved)^*****/*****
The sum of the first n cards is n(n+1)/2. To divide these number into three groups with the same sum, either n or n+1 mus be a multiple of 3. So this is not possible for n=4, 7, 10 and so on.
Here is a short list
n
2: 0
3: 0
5: 1 (5, 1-4, 2-3)
6: 1 (1-6, 2-5, 3-4)
8: 4
9: see answer to problem 1.
Now can you find a general formula for the number of possible groups?
Or for a simpler start: in how many ways can we draw cards from a series 1-n in such a way that that the sum is some given number?
Or: can you construct an algorithm that shows that the cards 1-3n (n>=2) can always be divided into three groups with the same sum?
I don’t have the answers to these questions, they just look interesting to me.

A new puzzle is published on Fridays, at least twice a month. You may check your solutions here.

The successor of the sultan (3)

August 6, 2021Deduction, LogicTeun Spaans

The ways in which the sultan of Buhrundipur choose his successor, were a bit, uh, unusual. He presented them with a series of tests. One by one he lead the into an empty basin with four doors.

Test 3^***/*****

“Only one door hides a treasure, the other doors hide a hungry shark. Oh, and only one label is true. Good luck!

Which box should the candidate open?

Complete this multiplication

July 30, 2021NumbersTeun Spaans

1) Complete this multiplication^**/*****
Fill in the missing numbers such that
54 x 2__ = ____8
is a correct multiplication and all the digits 0 – 9 are used exactly once.

This problem was published in the Dutch mathematics magazine Pythagoras, issue no 4 in year 9 (1970).

New puzzles are published at least twice a month on Friday.
You can find the solution here.

Fibonacci series

July 16, 2021ArithmeticTeun Spaans

Today’s puzzles were inspired by Michael Jacobs “Introductory Thinking Tasks”.

You all know the Fibonacci series: a term is the sum of the two previous terms, with the first two given. The top row shows a classic sequence:

Your task is of course to fill in the empty spaces of the other two rows.

The successor of the Sultan (2)

July 2, 2021Boolean logicTeun Spaans

The sultan took the survivors of the first round one by one to a second room with three boxes, depicted below. One was made of bronze, one of silver, and the third of gold.

Test 2^***/*****
He told them: One of the three chests holds a treasure. And exactly one of the labels on the boxes is true. You must open one of the boxes. No doubt it will comfort you that the poison of the snakes in the other two boxes are Naja mortiferum, the toxin of which is extremely painful and deadly, but very fast working, so you won’t suffer very long.

Which box should the candidate open?

The sum of the digits

June 18, 2021ArithmeticTeun Spaans

If you think that mathematics and arithmetic is something for boys, you probably never read about Shakuntala Devi. Born in 1929, as a young child she was taken by her father on road shows to display her abilities for mental calculation. At the age of six she demonstrated her abilities at the University of Mysore.

In 1977, when she must have been 48, at Southern Methodist University, she gave the 23rd root of a 201-digit number in 50 seconds.[6][4] Her answer, which was 546,372,891, was confirmed by calculations done at the US Bureau of Standards by the UNIVAC 1101 computer, for which a special program had to be written to perform such a large calculation, which took a longer time than for her to do the same.

She wrote several books, on puzzles, astrology, memory and homosexuality. What interests us here is the book “Puzzles to puzzle you”.
Here is one of them:
Which number is exactly 3 times the sum of its digits?

In her honor :
Which number is exactly 11 times the sum of its digits?

You can check your solution here

The successor of the Sultan (1)

June 4, 2021Boolean logicTeun Spaans

It was already known that the Sultan of Buhrundipur was a cruel men. It is only through recent research that we learnt how cruel. We already knew that the empire collapsed after his demise. He put all candidates whom he considered to be a possible successor through a series of tests, which have only now come to light.

Test 1^**/*****
There are 3 boxes, each with a label. One box holds a treasure, two boxes hold a deadly poison which is released when opening the box. One label tells the truth, the other two are lies.
Box 1: “This box holds a poison”
Box 2: “This box holds a treasure”
Box 3: “The label on box 2 is false”

Which box should the candidate open?