Question

Number of $5$-letter words that use letters from a $4$-letter set in which exactly one letter is missing

score 140 · Answer 1 · 2017-06-03 17:19:12

140

Views

Number of $5$-letter words that use letters from a $4$-letter set in which exactly one letter is missing

Published on 03 Jun 2017 - 17:19

score 38k · Answer 2 · 2017-06-04 09:56:56

38k

Views

How many numbers in between $1$ and $250$ are not divisible by $2, 3, 5$ or $7$?

Published on 04 Jun 2017 - 9:56

score 217 · Answer 3 · 2017-06-05 16:01:39

217

Views

Check proof that $|A \cup B \cup C| = |A| + |B| + |C| - (|A \cap B| + |A \cap C| + |B \cap C|) + |A \cap B \cap C|$

Published on 05 Jun 2017 - 16:01

score 69 · Answer 4 · 2017-06-05 22:14:17

69

Views

Prove $|(S_1 \cup S_2 \cup S_3)^c| =|U| - (|S_1| + |S_2| + |S_3|) + (|S_1 \cap S_2|+ |S_1 \cap S_3| + |S_2 \cap S_3|) - |S_1 \cap S_2 \cap S_3|$

Published on 05 Jun 2017 - 22:14

score 123 · Answer 5 · 2017-06-10 20:53:58

123

Views

Use PIE to count the number of $6$-multisets of $[6]$ in which no digit occurs more than twice.

Published on 10 Jun 2017 - 20:53

score 476 · Answer 6 · 2017-06-19 04:36:40

476

Views

Special case in inclusion exclusion principle

Published on 19 Jun 2017 - 4:36

score 241 · Answer 7 · 2017-06-22 18:35:15

241

Views

Use Inclusion-Exclusion to find the number of arrangements of 4 A's, 5 B's, 6 C's, 7 D's , 8 E's with exactly 2 adjacent C's

Published on 22 Jun 2017 - 18:35

score 393 · Answer 8 · 2017-06-30 02:28:46

393

Views

Proving an equality regarding fully independent events

Published on 30 Jun 2017 - 2:28

score 672 · Answer 9 · 2017-07-01 22:21:10

672

Views

Find the number of permutations of $1,2,3...,n$ such that $a_{i+1}\neq a_i+1$ for $ i<n $ if $a_i$ is the i-th element in the permutation?

Published on 01 Jul 2017 - 22:21

score 511 · Answer 10 · 2017-07-03 22:19:58

511

Views

How many 8-bit strings don't have 6 consecutive 0s?

Published on 03 Jul 2017 - 22:19

score 2.8k · Answer 11 · 2017-07-08 22:33:45

2.8k

Views

Solution Verification: How many positive integers less than $1000$ have at least one digit that is a $9$?

Published on 08 Jul 2017 - 22:33

score 390 · Answer 12 · 2017-07-16 17:04:11

390

Views

How many permutations of [9] are there in which exactly 5 numbers are in their original position?

Published on 16 Jul 2017 - 17:04

score 818 · Answer 13 · 2017-07-17 14:10:39

818

Views

How many ways are there to arrange pairs so that no two enemies are next to each other.

Published on 17 Jul 2017 - 14:10

score 61 · Answer 14 · 2017-07-25 04:34:39

61

Views

Inclusion-Exclusion Principle; why is this wrong?

Published on 25 Jul 2017 - 4:34

score 1k · Answer 15 · 2026-03-25 10:55:47

1k

Views

Platonic solids: duality. What is meant by "reversing inclusion"?

Published on 25 Mar 2026 - 10:55

List Question

Number of $5$-letter words that use letters from a $4$-letter set in which exactly one letter is missing

How many numbers in between $1$ and $250$ are not divisible by $2, 3, 5$ or $7$?

Check proof that $|A \cup B \cup C| = |A| + |B| + |C| - (|A \cap B| + |A \cap C| + |B \cap C|) + |A \cap B \cap C|$

Prove $|(S_1 \cup S_2 \cup S_3)^c| =|U| - (|S_1| + |S_2| + |S_3|) + (|S_1 \cap S_2|+ |S_1 \cap S_3| + |S_2 \cap S_3|) - |S_1 \cap S_2 \cap S_3|$

Use PIE to count the number of $6$-multisets of $[6]$ in which no digit occurs more than twice.

Special case in inclusion exclusion principle

Use Inclusion-Exclusion to find the number of arrangements of 4 A's, 5 B's, 6 C's, 7 D's , 8 E's with exactly 2 adjacent C's

Proving an equality regarding fully independent events

Find the number of permutations of $1,2,3...,n$ such that $a_{i+1}\neq a_i+1$ for $ i<n $ if $a_i$ is the i-th element in the permutation?

How many 8-bit strings don't have 6 consecutive 0s?

Solution Verification: How many positive integers less than $1000$ have at least one digit that is a $9$?

How many permutations of [9] are there in which exactly 5 numbers are in their original position?

How many ways are there to arrange pairs so that no two enemies are next to each other.

Inclusion-Exclusion Principle; why is this wrong?

Platonic solids: duality. What is meant by "reversing inclusion"?

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