User pwerth

21 votes

The total number of subsets is $2^n$ for $n$ elements

answered Jan 9, 2019 at 22:25

10 votes

Accepted

Derivative of absolute function

answered Jun 21, 2017 at 14:19

9 votes

Accepted

Derivative of $\sqrt{x^{2}}$ at $x=0$

answered Jan 17, 2019 at 18:24

9 votes

Accepted

How to add numbers with same base but unknown exponents?

answered Jan 22, 2019 at 17:19

8 votes

Accepted

What is the probability that, when 3 couples are seated around a circular table, no couple sits together?

answered May 7, 2014 at 3:31

7 votes

Accepted

Prove that the set $\Big\{ 1/(n+1): n \in \mathbb{N} \Big\} \cup \big\{ 0 \big\} $ is closed.

answered Aug 25, 2017 at 14:41

7 votes

Two players alternate flipping a coin until the result is head. How to derive that the probability for the first player to win is $2/3$?

answered Feb 8, 2019 at 16:43

5 votes

Accepted

Prove that $\frac{k^7}{7}+\frac{k^5}{5}+\frac{2k^3}{3}-\frac{k}{105}$ is an integer.

answered Jan 16, 2019 at 17:36

5 votes

How to show $ {n \choose m}{m \choose k}={n \choose k}{n-k \choose m-k}$ by counting pairs of sets $(A,B)$ in two ways

answered Jul 5, 2017 at 20:15

5 votes

Finding the least value of $y=3^{x-1}+3^{-x-1}$

answered Jul 18, 2017 at 15:57

5 votes

Find the natural numbers $n$ in which $n^2$ divides $584$?

answered May 8, 2014 at 19:55

5 votes

Solve for $m$: $m^5 + 7m + 8 \equiv 0 \pmod 3$

answered Dec 17, 2018 at 18:00

5 votes

Index of summation - integer?

answered Jan 4, 2019 at 20:07

5 votes

Prove that $A$ is invertible iff $\det(A)\neq 0$ with Cauchy-Binet theorem.

answered Jan 9, 2019 at 19:42

4 votes

Hoeffding's Inequality Probability $>1$

answered Dec 23, 2018 at 2:53

4 votes

Rolling $4$ dice and multiplying the results. What is the probability that the product is divisible by $5$ or has $5$ as the least significant digit?

answered Jan 11, 2019 at 19:06

4 votes

Accepted

Expressing A Strange Irrational Number As An Infinite Sum

answered Jan 31, 2019 at 16:41

4 votes

A game with a die and a watch

answered May 17, 2019 at 16:49

4 votes

Accepted

Suppose that $a=\binom70+\binom73+\binom76,b=\binom71+\binom74+\binom77,c=\binom72+\binom75$. How to algebraically compute $a^3+b^3+c^3-3abc$?

answered May 10, 2019 at 15:43

3 votes

Accepted

A question about integer BMO 1984 Question 4

answered Feb 8, 2019 at 17:41

3 votes

Accepted

Intermediate Value Theorem Proofs

answered Jan 11, 2019 at 21:03

3 votes

Accepted

Understading the Big-oh notation

answered Jan 12, 2019 at 18:53

3 votes

Accepted

Choosing an integer that is most likely to be the sum of die rolls

answered Jan 11, 2019 at 18:52

3 votes

Find the maximum number of points of intersection of 6 circles.

answered Jan 25, 2019 at 17:57

3 votes

What is the strongest statement that can be deduced, using Chebyshev’s inequality, about $p$?

answered Jan 22, 2019 at 18:03

3 votes

Accepted

Possible eigenvalues of a matrix satisfying $A*A = 4A$

answered Jan 22, 2019 at 18:42

3 votes

Prove $f$ is decreasing?

answered Jan 16, 2019 at 19:44

3 votes

Accepted

Finding E(YX) from a table

answered Jan 22, 2019 at 16:07

3 votes

Determining the length of a curve using integrals

answered Dec 25, 2018 at 22:22

3 votes

Accepted

$4 \times 4$ matrix and homogeneous system of equations.

answered Dec 18, 2018 at 7:10

Stack Exchange Network

137 Answers

The total number of subsets is $2^n$ for $n$ elements

Derivative of absolute function

Derivative of $\sqrt{x^{2}}$ at $x=0$

How to add numbers with same base but unknown exponents?

What is the probability that, when 3 couples are seated around a circular table, no couple sits together?

Prove that the set $\Big\{ 1/(n+1): n \in \mathbb{N} \Big\} \cup \big\{ 0 \big\} $ is closed.

Two players alternate flipping a coin until the result is head. How to derive that the probability for the first player to win is $2/3$?

Prove that $\frac{k^7}{7}+\frac{k^5}{5}+\frac{2k^3}{3}-\frac{k}{105}$ is an integer.

How to show $ {n \choose m}{m \choose k}={n \choose k}{n-k \choose m-k}$ by counting pairs of sets $(A,B)$ in two ways

Finding the least value of $y=3^{x-1}+3^{-x-1}$

Find the natural numbers $n$ in which $n^2$ divides $584$?

Solve for $m$: $m^5 + 7m + 8 \equiv 0 \pmod 3$

Index of summation - integer?

Prove that $A$ is invertible iff $\det(A)\neq 0$ with Cauchy-Binet theorem.

Hoeffding's Inequality Probability $>1$

Rolling $4$ dice and multiplying the results. What is the probability that the product is divisible by $5$ or has $5$ as the least significant digit?

Expressing A Strange Irrational Number As An Infinite Sum

A game with a die and a watch

Suppose that $a=\binom70+\binom73+\binom76,b=\binom71+\binom74+\binom77,c=\binom72+\binom75$. How to algebraically compute $a^3+b^3+c^3-3abc$?

A question about integer BMO 1984 Question 4

Intermediate Value Theorem Proofs

Understading the Big-oh notation

Choosing an integer that is most likely to be the sum of die rolls

Find the maximum number of points of intersection of 6 circles.

What is the strongest statement that can be deduced, using Chebyshev’s inequality, about $p$?

Possible eigenvalues of a matrix satisfying $A*A = 4A$

Prove $f$ is decreasing?

Finding E(YX) from a table

Determining the length of a curve using integrals

$4 \times 4$ matrix and homogeneous system of equations.