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Questions tagged [number-property]

Puzzles that use number properties such as even and odd, multiples of numbers, part of a well-known sequence (i.e. Fibonacci) or theorem (Pythagorean relations) or others in part of the method to solve the question.

8
votes
8answers
981 views

What mysterious whole number am I?

From my second point of view I copy that amount of first. I am the dominant side of two but for many I'm the worst. I'll be tricky to find but today might be your day, after all my neighbour is 2/3 of ...
9
votes
2answers
990 views

Ten-digit number that satisfy divisibilty rules for 2,3,4,5,6,7,8,9,10&11

Question: Arrange the digits 1,2,3,4,5,6,7,8,9,0 to make a ten-digit Number that satisfies all of the divisibility rules for 2,3,4,5,6,8,9,10,&11. BONUS: make the number also divisible by 7
5
votes
2answers
167 views

Using 20, 17, 16, 8, 7 to make 9

You can use $+, -, \times, $ or $/$ (namely $\div$). Use all five numbers (20, 17, 16, 8, and 7) only once to make $9$. From what I've been told there are $4$ answers. The only one I've been able ...
8
votes
4answers
308 views

A “Find the Path” Puzzle

I invented a puzzle, inspired by Simon Tatham's Portable Puzzle Collection. Is there anything that it could improve on? Was it too easy, or was it too hard? Anything I could add? What must I call it? ...
6
votes
8answers
498 views

Make $1,\dots,15$ using $3, 9, 9, 9$

This was inspired by many puzzles that use three/four numbers to create other numbers. I chose these numbers in particular because of this post. Can you find a way to make all the natural numbers ...
8
votes
2answers
221 views

Half and Double Value

A 3 year old child tried to input or copy a number (written on the paper) to a calculator but he messed up with the digit places. All the digits are there but the value of the number he inputed ...
10
votes
1answer
158 views

What is a Voluminous Number™?

In the spirit of the What is a Word™/Phrase™ series started by JLee, a special brand of Phrase™ and Word™ puzzles. If a number conforms to a special rule, I call it a Voluminous Number™. Use the ...
2
votes
3answers
351 views

72 + 96 = 120, is it possible?

I came across the following riddle: How is it possible for $72+96=120$ to be correct?
3
votes
1answer
155 views

systematic number removal [duplicate]

The whole, natural numbers 1 through 50 are written on a board. The following operation is performed 49 times: select any two of the numbers on the board and write the absolute value of their ...
17
votes
3answers
4k views

Which two students spoke wrongly? [duplicate]

A teacher wrote a large number on the board and asked the students to tell about the divisors of the number one by one. The 1st student said, "The number is divisible by 2." The 2nd student said, "...
6
votes
1answer
238 views

What do numbers have?

Numbers 0 through 9 each have a number of something. 0 has 6. 1 has 2. 2 has 5. 3 has 5. 4 has 4. How many do 5, 6, 7, 8 and 9 have?