Questions tagged [arithmetic]

For puzzles involving addition, subtraction, multiplication, or division.

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4
votes
1answer
246 views

What is the Sixth Number?

I'm thinking of 4 real numbers, $a,b,c$ and $d$ (they need not be integers, or even rational). There are 6 products you can make by multiplying pairs of these numbers, namely, $ab,ac,ad,bc,bd$ and $cd$...
34
votes
4answers
3k views

Display a number using a scientific calculator with most keys are stuck

Your have a scientific calculator such that most of the keys are unable to be pressed. The only keys that work are those for the functions $$ x^2 \;\; \sqrt{x} \;\; x!\;\; \exp\;\; \ln\;...
5
votes
1answer
767 views

Fit numbers on a grid with required sums for squares

Can anyone solve this puzzle or give me some tips? Rules: you have to use all 1, 2, 3, 4, 5, 6, 7 numbers in every 8 straight and vertical lines(4 vertical line and 4 straight line) And the summation ...
12
votes
1answer
833 views

Poring Over the Numbers: A Hidden Message

I thank my lucky stars I'm able to write this to you. I spent a hefty percentage of my remaining cash at the courier's office and I want to underscore the importance of this communique. If a man comes ...
2
votes
4answers
1k views

The Twins with a Different Age

Warning: To answer this riddle you need to have a thorough understanding of how time works. Two twins were born during the same year, on the same month, and the same day, exactly 10 minutes apart. ...
6
votes
2answers
2k views

Find the age of the ship and of the boiler

Some years back I was travelling by a cargo ship from New Zealand to Tahiti. I was curious to look around the ship one day and in the boiler room I asked a man how old the ship was. He smiled and ...
4
votes
3answers
606 views

A Second Benjamin Button

This was inspired by A curious case of Benjamin Button but has a different solution. In 1980 AD (or 1980 CE, if you prefer), Jack has an age of 20. In 1985 however, he is only 6 years old. How did ...
6
votes
1answer
504 views

A curious case of Benjamin Button

In 1980, Jack has an age of 20. In 1985 however, he is only 15 years old. How did he age backwards?
6
votes
2answers
532 views

Odd birthdate surprise

Last year, just before my birthday in February, I noticed something unsual. The last two digits of my birth year were the same as my age. How old was I then and was this an unusual occurrence?