Use this tag when you want to determine the thinking that is needed to solve a certain type of problem, as opposed to looking for a specific answer to a question.

learn more… | top users | synonyms

1
vote
1answer
12 views

Asymptotic stopping time for a ball-drawing problem

Take two different boxes, one with $N$ red balls and one with $N$ blue balls. Remove balls one at a time from either box with equal probability. When only one color is left, the (expected value of ...
2
votes
0answers
25 views

How to learn problem solving strategy for Measure Theory?

I have taken both graduate level Algebra and Measure theory courses but found the latter much more difficult for me. I have put a lot effort on learning it by reading a few reference books and ...
0
votes
2answers
15 views

Units of Measure conversion

I was wondering if i could get some help trying to create a simple math formula. I recently was given an interview to work as a tier1 programmer and was asked to make a program. I made the whole thing ...
0
votes
0answers
6 views

Getting number of detractors/passive responses with only NPS and number of responses.

I have survey data that's computed as: NPS = (a - c)/ (a + b + c) where: a = positive resopnse ...
0
votes
0answers
26 views

Argument for finite solution of power Diophantione Equation.

Assume the equation $4x^3=y^2+3$ has infinite positive integer solution. If $x,y$ has general solution then it is clear that for any $x$(rational, integer), there is a $y$. It can be said there is a ...
6
votes
3answers
470 views

High-School level probability and logic problem

So the other day I took a math test, (not for class, its just an optional test, so this isn't and kind of cheating) which included all kinds of logical and problem solving exercises, among others this ...
2
votes
3answers
127 views

Is it possible to solve the Zebra Puzzle/Einstein's Riddle using pure math?

A coworker of mine posted a problem in our local communication software that seems to be a simpler variation of the Zebra Puzzle/Einstein's Riddle. I know how to solve it intuitively, by using ...
0
votes
2answers
26 views

Finding the probability of a complex event…

My apologies - I'm not a math professional, but the guys in my office (a bunch of web programmers) just came across across a logic problem that we've been discussing. We have a solution, but now ...
1
vote
0answers
32 views

Combination problems

During numerous math contests I have come across questions such as: I have __ shirts, __ shoes and ___ pants... How many combinations of the __ are possible... As well as many other combination ...
3
votes
1answer
52 views

What are some good problem solving techniques for Math Olympiad style tests? [duplicate]

I am taking part in a Math Olympiad style test at my school in a few weeks. This test is mainly problem solving based and tests you on topics such as counting techniques, algebra, geometry as well as ...
1
vote
1answer
24 views

Where do I begin to solve this ODE?

I've a problem: $ye^{xy}+4y^3+(xe^{xy}+12xy^2-2y)y'=0 $ I can't begin to solve it because I don't know where to start. Help me, please. Thanks!
-1
votes
0answers
25 views

Expected value problem

Imagine the following scenario: Several players contribute coins to a pot in a random order and without knowing what other players have contributed. When every player has added his stake, the coins ...
1
vote
1answer
50 views

How is problem solving ability on an olympiad level relevant to mathematical graduate study/research?

I am starting on math later than many of my peers and hence have little to no experience in competitive problem solving. Is this a disadvantage during the study of the more abstract mathematics that ...
5
votes
3answers
678 views

Dates with 8 consecutive digits

In many places, dates are written as DD/MM/YYYY. For example, the 25th of April 1736 is written as 25/04/1736. Dates such as this one that use 8 consecutive digits (not necessarily in order) will be ...
1
vote
0answers
37 views

Ideas for math problem solving class for undergraduate students in university

In our university there is a huge gap between two group of students. a group of them came from Math Olympiad competitions and have a very strong background from high school but others, they have just ...
1
vote
2answers
38 views

How can I reduce the occurrence of algebra mistakes in my solutions?

Apologies is this is the wrong forum; point me to the right one if that's the case. In this particular case, I'm studying limits (in an intro Calc course, and on Khan Academy) but the question ...
0
votes
2answers
16 views

How to find average walking time per day

I have calculated that the total walking time for a person is 2990702 minutes in 801 days. I want to know his average walking time per day in minutes. I dont know if I need to convert minutes into ...
0
votes
2answers
23 views

Number of ways to ride from one city to another

I stucked with some combinatorial problem: There are 3 highroads between city A and city B. Highroads are intersected with 4 countryroads. What is the number of ways to make a tour from A to B, if we ...
1
vote
1answer
27 views

Help finding the inverse of an exponential function

$$f(x)=6^{3x+9}-2.$$ I got to one step, but I became lost. I understand that I'm converting it into logarithmic form, but I don't understand what the next steps are. \begin{align*} ...
0
votes
0answers
14 views

solving a linear equation in a mixture problem [closed]

my question is about word problem: two alcohol solutions of 20% salt solution is mixed with 4 gallons of 50% salt solution. determine the percentage of salt solution in the new mixture.
2
votes
1answer
35 views

If for every k the interval $[a,ak]$ contains $n$ specials numbers how many special numbers $[az,akz]$ must contain?

The purpose of my question is to determine if a specific kind of reasoning is true or false. Let's say that for every positive natural number $a$, there is a at least $n$ "special numbers" in the ...
1
vote
0answers
24 views

Can we choose $g$ so that $\|(g\widehat{(f^{3})})^{\vee}\|_{L^{p}} \leq C \|g_{1}f\|_{L^{2}}^{r} \|(g_{2}\hat{f})^{\vee}\|_{L^{s}}$?

Let $f, f^{2}, f^{3}\in L^{q}(\mathbb R)\cap C_{0}(\mathbb R)$ where $ q\geq p, \ \text{and}$ and $C_{0}(\mathbb R)$ is the class of continuous functions vanishing at infinity. My Questions: ...
0
votes
0answers
12 views

What is the fastest way to calculate the character of a fundamental representation?

Suppose we know the Cartan matrix $C$ of a Kac-Moody algebra $\mathbb g$: $$ C=\left(\begin{array}{cccc} 2 & -1 & 0 & 0\\ -1 & 2 & -1 & -1\\ 0 & -1 & 2 & 0\\ 0 ...
7
votes
1answer
78 views

A “Theorem Style” Problem Book in Differential Geometry

I am trying to teach myself differential geometry using Lee's Introduction to Smooth Manifolds. To test my understanding, and learn the subject better, I am looking for a good problem book in ...
1
vote
1answer
46 views

Coin Flipping Game - Expected Number of Tails

Can someone help me with this problem? In this game, let $S_{t}$ denote your earnings at time $t$. Your initial earnings is one dollar ($S_{0} = 1$). For each subsequent time, $t = 1, 2, ..$, flip a ...
3
votes
1answer
59 views

Trying to solve $A^TA = B$ where $B$ is known

Have a matrix A that's 4x3 and a matrix B that is known. They relate by the following equation: $$ A^T A = B $$ Trying to find A, given B, such that $A^TA$ is as close to B as possible. I've tried ...
0
votes
1answer
15 views

How to stabilize cyclic tridiagonal matrix algorithm?

I've received a task which is: Solve equation by cyclic tridiagonal matrix algorithm: $$ \frac{\partial{f}}{\partial{t}} = \lambda*\frac{\partial{f}}{\partial{x}}, \\ x\in[0,1]\ t\in[0,1] \\ ...
2
votes
1answer
54 views

Problem Books with Problems less “intense” than Putnam Problems

As the title indicates, I'm looking for a few suggestions on problem books. The problems should be a bit less demanding than Putnam problems. Like the Putnam, however, the prerequisites should be ...
3
votes
2answers
25 views

Calculating the value of numbers with different operations

Calculate the value of: $$-14 + 49 \times 21 - 63 + 56 \div 35 \div 28 \times 70 - 42 \div 7$$ I noticed the numbers are a factor of $7$, so I took out $7$ as a common factor: $$7[-2 + (7 \times 3) ...
1
vote
0answers
12 views

Scheduling problem

Consider the following setting: $N$ jobs, each has a starting time, which is assumed to be a natural number and all N numbers are distinct, e.g., the 1st job has starting time at 5, the 2nd is 6, the ...
3
votes
0answers
29 views

Good problem books at a relatively advanced level?

I have been searching for problem books on advanced topics. By advanced I am referring to the undergraduate level and above. I am looking for something analogous to the olympiad type problem books ...
1
vote
1answer
38 views

Series solution

Given the differential equation $2(1-x)y''-3y'+\frac{y}{x}=0$ and in standard form: $y''-\frac{3}{2(1-x)}y'+\frac{1}{2x(1-x)}y=0$ I want to find the series solution for the larger root $σ = 1$ of ...
2
votes
1answer
58 views

Rank of a symmetric matrix. (ISI Sample Paper)

I have rephrased the question as follows : Here, $\langle v,w\rangle=v^tw$ is the usual dot product. Let $A$ be an $n \times n$ symmetric matrix. Let $l_1, l_2, \ldots , l_{r+s}$ be $(r + s)$ ...
5
votes
0answers
34 views

How to find a list of summands and factors adding up to a total?

I am neither a mathematician nor do I have an idea on how to write down my problem in accurate mathematic formulas. Please feel free to edit my question into shape and remove this paragraph. Also I am ...
0
votes
2answers
37 views

Homework Problem About Finding a Value of $k$ for Which the Given System of Equations Has No Solutions

While working through the third of three packets I'm going through to review for a pre-test for an independent-study calculus class, I came across the following problem: For what value of $k$ ...
2
votes
1answer
45 views

mod operation proof

Prove: $ ab\,\bmod\,d = ((a\,\bmod\,d)\,(b\,\bmod\,d))\,\bmod\,d $ where $a$, $b$ and $d$ are non-negative integers. Reference : http://en.wikipedia.org/wiki/Modulo_operation#Equivalencies Context ...
1
vote
1answer
52 views

Find all continuous functions $f:\mathbb{R}\to\mathbb{R}$ satisfying $\frac{f(x+3)}{3+f(x)}=\frac{4+x^2}{x^2}$

Find all continuous $f:\mathbb{R}\to\mathbb{R}$ satisfying $$\frac{f(x+3)}{3+f(x)}=\frac{4+x^2}{x^2}.$$ I believe the original question was $$\frac{f(x)}{3+f(x)}=\frac{4+x^2}{x^2},$$ which has a ...
1
vote
1answer
38 views

Polygon center which always lies inside the polygon (with no hole)

Is there is any type of centre (of polygon) which always lies inside the polygon (with no hole)? Note: Here our polygon may be any type of polygon (convex or concave) but ...
1
vote
1answer
54 views

Can you generate math problems that are solveable?

If you take Linear Programming, it problems are formulated like this: You know that Cabinet X costs 10 cents per unit, requires 6 square feet of floor space, and holds 8 cubic feet of files. ...
0
votes
1answer
34 views

Odds of Winning Office NCAA Pool

I have 6 coworkers competition in a NCAA bracket. I'm trying to find out how to calculate who has the best chance of winning. For example currently the score card looks like: Player 1. Current Right ...
2
votes
1answer
73 views

Solving an equation for x, characteristics

I am trying to plot characteristics on Matlab for a hyperbolic pde. I need to compute \begin{equation} x=\frac{t}{(1+x^2)}+x_i \end{equation} for every spatial step. Any help with how to do this? ...
2
votes
1answer
28 views

Problem about sum of polynomials

I have this problem I don't know how to solve: Let $f(x)$ be a polynomial of degree $n$ with real coefficients and such that $f(x) \geq 0 \forall x \in \mathbb{R}.$ How do I show that $f(x) + f'(x) + ...
0
votes
1answer
30 views

Some clarifications and a question on basic probability.

I have a few questions and some clarifications. CLARIFICATIONS: 1. Assume we roll 2 four sided dice. What is P({sum of the rolls is even})? I answered the question correctly I: Odd + Odd = Even J: ...
2
votes
2answers
62 views

$\lim_{n\to\infty}a_nb_n=? $ given that $\lim_{n\to\infty}a_n=0$ and $\lim_{n\to\infty}b_n=\infty$

A. $\lim_{n\to\infty}a_nb_n=?$ given that $\lim_{n\to\infty}a_n=0$ and $ \lim_{n\to\infty}b_n=\infty$ B. $\lim_{n\to\infty}{a_n \over b_n}=?$ given that $\lim_{n\to\infty}a_n=0$ and ...
2
votes
2answers
75 views

Minimize : $\sqrt{(1+{1\over a})(1+{1\over b})}$ subject to $a+b=\lambda$.

Given positive real variables $a$ and $b$, find the minimum of $$f(a,b)=\sqrt{\left(1+{1\over a}\right)\left(1+{1\over b}\right)}$$ subject to $a+b=\lambda$ where $\lambda$ is a constant . [ISI ...
0
votes
1answer
17 views

Non-convex quadrilateral and pentagon?

Is it possible to draw a non-convex quadrilateral/pentagon and an additional straight line such that the straight line cuts through the interior of each of the quadrilateral/pentagon's edges?
0
votes
1answer
25 views

A question about subspace and finding basis

guys help me I couldn't solve this question I've been working on subspaces for sometime but still cant do this kind of questions.
0
votes
2answers
23 views

Surface Area and Volume relationship

I know that the $SA = 6s^2$ and that the volume is equal to the base $x$ the $side = s^3$. However, I'm not sure how to approach this though.
0
votes
1answer
22 views

How does one find the change?

I tried using ratios but I failed. I need to subtract one to get the correct answer. I remember finding the change before, but I've forgotten how to. Any hints?
4
votes
1answer
54 views

Prove that following polynomial has no non-zero real solution.

Prove that following equation has no non-zero real solution. $$ \sum_{ 1 \leq n \leq 120,\, 2|n \;\textrm{or}\; 3|n } x^n = 0$$ Any idea?