Question

How many 4 digit numbers can be formed from digits 0 to 9 without repetition which are divisible by 5?

score 3.2k · Answer 1 · 2026-04-14 02:57:20

3.2k

Views

How many 4 digit numbers can be formed from digits 0 to 9 without repetition which are divisible by 5?

Published on 14 Apr 2026 - 2:57

score 2k · Answer 2 · 2026-04-16 12:45:43

2k

Views

How many 3 -digit numbers can be formed from 0 to 8 whose sum is equal to 20 for repetition and non-repetition?

Published on 16 Apr 2026 - 12:45

score 87 · Answer 3 · 2026-04-15 10:11:31

87

Views

Prove $3^{n−2} n (n − 1) = \sum_{k=2}^{n} \binom{n}{k} (k)(k − 1)2^{k−2}$ for $n\ge3$

Published on 15 Apr 2026 - 10:11

score 161 · Answer 4 · 2026-04-16 04:16:19

161

Views

Number of lattice paths from $(0, 0)$ to $(n, m)$ that make exactly $k$ turns

Published on 16 Apr 2026 - 4:16

score 106 · Answer 5 · 2026-04-17 04:59:49

106

Views

How many ways to place A's and B's.

Published on 17 Apr 2026 - 4:59

score 598 · Answer 6 · 2026-04-11 10:09:17

598

Views

Combinatorics Problem - Ranking Athletes by Nationality

Published on 11 Apr 2026 - 10:09

score 100 · Answer 7 · 2026-05-13 01:44:02

100

Views

Simplifying $ \sum_{1\cdot m_1 + 2\cdot m_2 + \cdots + n \cdot m_n = n} \frac{1}{m_1 ! m_2 ! \cdots m_n !} t^{m_1 + \cdots + m_n} $

Published on 13 May 2026 - 1:44

score 582 · Answer 8 · 2026-05-11 06:32:07

582

Views

Calculate probability using inclusion-exclusion and deduce formula for binomial coefficicient

Published on 11 May 2026 - 6:32

score 108 · Answer 9 · 2026-04-11 04:27:42

108

Views

Filling $N$ boxes with $K$ balls without using the Boole inequality.

Published on 11 Apr 2026 - 4:27

score 634 · Answer 10 · 2026-04-14 23:15:40

634

Views

In how many ways can one pick 6 cards from a deck of 52 cards so that all suits are present?

Published on 14 Apr 2026 - 23:15

score 83 · Answer 11 · 2026-04-16 21:29:11

83

Views

What's the first non-planar graph of the first $n$ numbers where edges show divisibility?

Published on 16 Apr 2026 - 21:29

score 361 · Answer 12 · 2026-04-14 22:53:30

361

Views

Four-letter words that can be formed from the letters of the word "facetious" without letter duplication

Published on 14 Apr 2026 - 22:53

score 122 · Answer 13 · 2026-04-14 20:51:06

122

Views

Show by counting in two ways that $\sum_{k=0}^{n} \binom{n+k}{k} = \sum_{k=0}^{n} 2^{k} \binom{n}{k}$?

Published on 14 Apr 2026 - 20:51

score 78 · Answer 14 · 2026-04-09 08:35:49

78

Views

Applied Combinatorics Question on arrangements

Published on 09 Apr 2026 - 8:35

score 963 · Answer 15 · 2026-04-11 00:26:35

963

Views

Arrangements of TINKERER with restriction

Published on 11 Apr 2026 - 0:26

List Question

How many 4 digit numbers can be formed from digits 0 to 9 without repetition which are divisible by 5?

How many 3 -digit numbers can be formed from 0 to 8 whose sum is equal to 20 for repetition and non-repetition?

Prove $3^{n−2} n (n − 1) = \sum_{k=2}^{n} \binom{n}{k} (k)(k − 1)2^{k−2}$ for $n\ge3$

Number of lattice paths from $(0, 0)$ to $(n, m)$ that make exactly $k$ turns

How many ways to place A's and B's.

Combinatorics Problem - Ranking Athletes by Nationality

Simplifying $ \sum_{1\cdot m_1 + 2\cdot m_2 + \cdots + n \cdot m_n = n} \frac{1}{m_1 ! m_2 ! \cdots m_n !} t^{m_1 + \cdots + m_n} $

Calculate probability using inclusion-exclusion and deduce formula for binomial coefficicient

Filling $N$ boxes with $K$ balls without using the Boole inequality.

In how many ways can one pick 6 cards from a deck of 52 cards so that all suits are present?

What's the first non-planar graph of the first $n$ numbers where edges show divisibility?

Four-letter words that can be formed from the letters of the word "facetious" without letter duplication

Show by counting in two ways that $\sum_{k=0}^{n} \binom{n+k}{k} = \sum_{k=0}^{n} 2^{k} \binom{n}{k}$?

Applied Combinatorics Question on arrangements

Arrangements of TINKERER with restriction

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