Question

How many numbers are there between $100$ and $1000$ such that every digit is either $2$ or $9$?

score 1.5k · Answer 1 · 2026-04-15 17:03:09

1.5k

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How many numbers are there between $100$ and $1000$ such that every digit is either $2$ or $9$?

Published on 15 Apr 2026 - 17:03

score 191 · Answer 2 · 2026-04-10 10:53:45

191

Views

Pigeonhole principle based algorithm

Published on 10 Apr 2026 - 10:53

score 102 · Answer 3 · 2026-04-23 23:48:34

102

Views

Translating and inflating a set of $k$-dimensional subspaces of $\mathbb F_p^n$ to form a cover by affine hyperplanes?

Published on 23 Apr 2026 - 23:48

score 420 · Answer 4 · 2026-04-14 20:03:06

420

Views

minor relation and topological minor relations are partial orderings of on the class of finite graphs

Published on 14 Apr 2026 - 20:03

score 52 · Answer 5 · 2026-04-15 13:15:08

52

Views

When Replacement doesn't matter (drawing marbles)

Published on 15 Apr 2026 - 13:15

score 559 · Answer 6 · 2026-04-12 13:09:29

559

Views

A game involving binomial probabilities

Published on 12 Apr 2026 - 13:09

score 58 · Answer 7 · 2026-04-14 01:08:04

58

Views

A game with rounds containing four people

Published on 14 Apr 2026 - 1:08

score 1.5k · Answer 8 · 2026-04-14 18:06:00

1.5k

Views

Combinatorics: Distinguishable and Indistinguishable Variables

Published on 14 Apr 2026 - 18:06

score 951 · Answer 9 · 2026-04-14 04:31:56

951

Views

Expected number of balls to pick to select three balls of the same colour

Published on 14 Apr 2026 - 4:31

score 354 · Answer 10 · 2026-04-17 03:53:06

354

Views

Find all $n \in \mathbb{N}$ such that ${{2n}\choose{n}} \equiv (-1)^n\pmod{2n+1}$

Published on 17 Apr 2026 - 3:53

score 458 · Answer 11 · 2026-04-17 13:37:25

458

Views

Colouring squares in a grid

Published on 17 Apr 2026 - 13:37

score 127 · Answer 12 · 2026-04-11 09:18:35

127

Views

In how many ways can N be written as a sum of positive numbers less or equal to K?

Published on 11 Apr 2026 - 9:18

score 507 · Answer 13 · 2026-04-14 08:41:34

507

Views

A question on counting the almost (!) injective monotone functions of two sets

Published on 14 Apr 2026 - 8:41

score 123 · Answer 14 · 2026-04-16 14:05:21

123

Views

How many different ways are there to pay exactly $20$ p using only $1$ p and $2$ p?

Published on 16 Apr 2026 - 14:05

score 41 · Answer 15 · 2026-04-17 10:15:00

41

Views

Counting the dimension

Published on 17 Apr 2026 - 10:15

List Question

How many numbers are there between $100$ and $1000$ such that every digit is either $2$ or $9$?

Pigeonhole principle based algorithm

Translating and inflating a set of $k$-dimensional subspaces of $\mathbb F_p^n$ to form a cover by affine hyperplanes?

minor relation and topological minor relations are partial orderings of on the class of finite graphs

When Replacement doesn't matter (drawing marbles)

A game involving binomial probabilities

A game with rounds containing four people

Combinatorics: Distinguishable and Indistinguishable Variables

Expected number of balls to pick to select three balls of the same colour

Find all $n \in \mathbb{N}$ such that ${{2n}\choose{n}} \equiv (-1)^n\pmod{2n+1}$

Colouring squares in a grid

In how many ways can N be written as a sum of positive numbers less or equal to K?

A question on counting the almost (!) injective monotone functions of two sets

How many different ways are there to pay exactly $20$ p using only $1$ p and $2$ p?

Counting the dimension

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