Questions on fractions, which are expressions (not values) of the form $\frac pq$.

learn more… | top users | synonyms

5
votes
1answer
39 views

Multiplication of algebraic fraction not giving desired result

I am having a try at solving this: that supposed to return: but I get stuck at: which can be written as
1
vote
2answers
49 views

Where did my simplification go wrong? Sum and difference formula simplification

I'm struggling with the following: We are to use the sum and difference formulas to find the exact value of the expression. The problem is simplification has been tough. As a last resort I decided to ...
0
votes
1answer
12 views

simple multiplication question: multiplying radial fractions

I'm having a bit of brain block right now. In order to multiply any fractions you simply reduce to lowest form, then multiply num., then denom. When I tried with fractions in radian form it didn't ...
0
votes
2answers
36 views

A reduction of $10\%$…

A reduction of $10\%$ in the price of sugar would enable a man to buy $2\,\rm{kg}$ of sugar more for Rs. $125$. Find the reduced price per kg. My attempt: Let the initial price of sugar be Rs. $x$ ...
0
votes
0answers
16 views

Approximate ratio with a small fraction so that numerator multiplied by denominator give enough rectangular area?

I would like to layout given number of objects (like plots) into rectangular area (like computer operating system window on screen). I would like to calculate the width and height of the window (in ...
-3
votes
1answer
19 views

Fraction walk through [on hold]

$$0.824 = \frac{n/20\cdot 1}{n/20\cdot 1+(1-n/20)\cdot 0.5}$$ Source. Please answer this question with step by step. Thank you so much
1
vote
0answers
25 views

quotient of two differentiable functions is differentiable

I have two functions $k(t)$ and $l(t)$ in a certain closed interval $[a,b]$ both functions are continuous and differentiable in the interval. In addition we have: Both functions are increasing with ...
1
vote
4answers
53 views

Find the limit of fraction involving logarithms

I am looking for a way to prove the following limit for integer $x$s: $$\lim_{x\to\infty}{\frac{\log(x+2)-\log(x+1)}{\log(x+2)-\log(x)}}=\frac{1}{2}$$ I could find the result by using a computer ...
1
vote
0answers
19 views

Stern-Brocot Tree and sum of coefficients of continued fraction

Suppose we are given a continued fraction $$\frac{p}{q}=a_{1}+\frac{1}{a_{2}+\frac{1}{a_{3}+\frac{1}{a_{4}+\cdots}}}$$ I am trying to find an expression, possibly asymptotic, for the sum of the ...
3
votes
3answers
55 views

Basic algebra problem: $ \frac{\frac{1}{x}+\frac{1}{y}}{\frac{1}{x^2}-\frac{1}{y^2}} $

Basic algebra problem I can't seem to figure out: $$ \frac{\frac{1}{x}+\frac{1}{y}}{\frac{1}{x^2}-\frac{1}{y^2}} $$ $x,y \in \mathbb{R}, x^2 \neq y^2, xy\neq0$. Now I know the result is: ...
6
votes
2answers
5k views

Ratios make me feel like an idiot - help me mix up some Coca-Cola

I may be over-complicating things, but something doesn't seem right (and I swear this isn't homework, I'm friggin 30 years old :P). I want to see what it will cost me to make a TWO liter of Coca-Cola ...
0
votes
4answers
37 views

Simple Fraction needing explanation

$$\frac{x}{x^{-1/2}} = x^{3/2}$$ How? I don't see what is going on here. What rule is being used to achieve this amount?
2
votes
3answers
54 views

Why Doesn't $2^{1/n}= 1/(2^n)$

Take $2^{1/n}$. Since $1/n$ can be simplified as $n^{-1}$, the original term can become $2^{n^{-1}}$. The exponents can then be multiplied to result in $2^{-n}$ which is $1/(2^n)$. However it is ...
3
votes
1answer
56 views

Repeating decimal notation of 1/53 on WolframAlpha vs notation on Wikipedia

WolframAlpha shows for 1/53 $0.0\overline{1886792452830}$ as the repeating decimal. Why is it not $0.\overline{0188679245283}$ instead? For example, Wikipedia shows for 1/81 ...
1
vote
0answers
38 views

Is this a mistake on my part or theirs?

I'm not sure if I'm the one making the mistake, or my math book. It looks like the negative sign completely disappeared. $$\frac{3x^2}{-\sqrt{18}} \cdot \frac{\sqrt{2}}{\sqrt{2}} = ...
20
votes
9answers
2k views

How to find irrational numbers between rationals. (And is my method correct?)

I have a question from an A-level revision book: Find an irrational number which lies between $\frac34$ and $\frac78$. What is the correct method for doing this? Here is my method: Square ...
1
vote
3answers
30 views

How do you solve B and C for $\frac{s-1}{s+1} \frac{s}{s^2+1} = \frac{A}{s+1} + \frac{Bs+C}{s^2+1}$?

How do you solve B and C for $\frac{s-1}{s+1} \frac{s}{s^2+1} = \frac{A}{s+1} + \frac{Bs+C}{s^2+1}$ ? $A = \left.\frac{s^2-s}{s^2+1} \right\vert_{s=-1} = \frac{1-(-1)}{1+1}=1$
3
votes
1answer
39 views

Simple formula for the $n$-ary version of $(x,y) \mapsto \frac{x+y}{1-xy}$

Let $x * y = \frac{x + y}{1 - xy}$. I want a single formula for $x_1 * x_2 * \ldots * x_n$, for all natural $n$. In order to generate plausible candidates, let's see what happens at small values of ...
-1
votes
1answer
61 views

The name of the sum $\sum_{i=0}^n \frac{1}{m-i}$

Sorry for the vague question name, since I am looking for the name of the series. Also this might not be a "series" by the strict definition of a series.. anyways here it is: Choose some $m$ and $n$ ...
-1
votes
2answers
38 views

World Problem Math Algebra Fraction

The denominator of a fraction in simplest form is greater than the numerator by $3$. If $7$ is added to the numerator, and $5$ added to the denominator, then the fraction itself is increased by ...
0
votes
1answer
37 views

Partial fraction integration with unclear roots

Let's look at a simple example like $\frac{1}{x^3+2x+1}$ here. We know that the denominator has a real root between $0$ and $-1$ (could go closer, but that's not the point). By the concept of slope of ...
0
votes
2answers
39 views

Partial fraction in two variable problem

How to write partial fraction of $$\frac{12m-n-3mn+7}{5m-2n-2mn+5}$$ I just write first and second denominator: $5-2n$ and $m+1$.
0
votes
1answer
15 views

Ratio of sums vs sum of ratio

Is anyone aware of any general (or perhaps not so general) relationship (inequality for instance) relating $A(x,y)= \frac{\sum_z f(x,y,z)}{\sum_z g(y,z)}$ and $B(x,y)= ...
3
votes
3answers
56 views

How to articulate where the extra 1 came in this easy question

"Albert owns 5/9ths of the stock in the North West Chocolate Company. His sister, Rena, owns half as much stock as Albert. What part of stock is owned by NEITHER Albert nor Rena?" The answer is ...
2
votes
1answer
27 views

Is it correct? Prove that any fraction can be reduced

I want to know if my prove is correct. My goal is proving: Hypothesis: $a,b \in \mathbb Z$ and $a,b \notin \{-1, 0, 1\}$. Thesis: for all $ a, b$, exist $a',b'\in \mathbb Z$ that verify ...
2
votes
1answer
20 views

About a largest integral value of this sum of reciprocal numbers.

In a test , I was asked to solve the following question : If $a_1,a_2,a_3, \cdots ,a_n$ are $n$ distinct odd natural numbers and not divisible by any prime number greater than equal to $7$ . Then the ...
2
votes
3answers
58 views

Solve fractions multiplication

I believe this is a very simple one, but I simply can't figure it out. How to solve? $$\frac12\cdot\frac34\cdot\frac56\cdots\frac{17}{18}\cdot\frac{19}{20}$$
3
votes
2answers
64 views

Laurent expansion of $\frac{1}{z^2}$

I need to find a Laurent expansion of $\frac{1}{z^2}$ with centre in $z_0 = 1$ and $P(1, 2014, 2015)$. If it was $\frac{1}{z}$, I'd rewrite the fraction like this: $$ \frac{1}{(z-1) +1 } $$ But ...
-2
votes
1answer
358 views

How to multiply, divide, add and subtract fractions

I've spent hours on this and I keep getting mixed answers. I need to know the rules for multipling, dividing, adding, subtracting equations involving fractions. I google search but the information is ...
3
votes
3answers
174 views

How to get from $\frac{x}{x+1}\;$ to $\;1 - \frac{1}{x+1}$?

Please show me how to manipulate $\dfrac{x}{x+1}\;\;$ to get $\;\;1 - \dfrac{1}{x+1}$
1
vote
4answers
80 views

How do I show that $-\frac{1}{e^x + 1} + 1 = \frac{e^x}{e^x + 1}$?

The expression is $$-\frac{1}{e^x + 1} + 1 = \frac{e^x}{e^x + 1}$$ I would like help to get from the left side to the right side.
-1
votes
2answers
46 views

If the chance of an event was $1/128$ and increased by $20\%$, what is the new chance?

So I have something that has a 1/128 chance of occurring, let's say. Suddenly, the chances of that thing happening are increased by 20%. How is that fraction written? Would you multiply 1/128 by ...
0
votes
1answer
25 views

Find original cost based on fractional purchase

How would I go about finding the original cost of bitcoin knowing that $20 purchased .0531401 of bitcoin? I would like to know what the cost of 1 bitcoin was at the time of purchase? ...
2
votes
3answers
4k views

What's the largest possible repeating decimal that can be created from a fraction (if n <= 9,999 & d <= 9,999)

What's the largest possible repeating decimal that can be created from a fraction if: The numerator has to be less than or equal to 9,999 The denominator has be less than or equal to 9,999? I know ...
2
votes
3answers
106 views

Solving equations including floor function.

I got a little trouble solving equations that involve floor function in an efficient way. For example : $$ \left\lfloor\frac{x+3}{2}\right\rfloor = \frac{4x+5}{3} $$ In the one above, I get that ...
5
votes
1answer
61 views

Question on recurring decimal digits

In my discrete maths class, I have come across an interesting phenomenon for which I can't find an explanation! If we divide $1$ by $13$ we obtain $0.07692307\ldots$ If we divide $3$ by $13$ we ...
3
votes
3answers
42 views

How to properly set up partial fractions for repeated denominator factors

I was just trying to solve a problem that had the following item which I needed to split into separate generating functions: $$\frac{x}{(1-2x)^2(1-5x)}$$ I had assumed I needed to split it into: ...
3
votes
1answer
32 views

Unit Fraction Addition

My teacher challenged us: "Can you express the fraction $55\over 108$ as the sum of two unit fractions$?$" I figured out that ${1\over 54} + {1\over 2} = {56\over 108}$ but I could not figure out a ...
1
vote
5answers
162 views

Proving that $\frac{a}{b} = \frac{c}{d}$ if and only if $ad = bc$

I was working on a problem which asked: Prove that $ \frac{a}{b} = \frac{c}{d} $ if and only if $ad=bc$, provided $c,d \neq 0$. Is it sufficient to manipulate $ \frac{a}{b} = \frac{c}{d} $ via ...
0
votes
2answers
32 views

How do we compare fraction without changing to a similar denominator?

This is Singapore Mathematical Olympiad 2015 Grade 8/Secondary 2 Junior Round 1 Question 1. 1.Among the five numbers, $\frac{5}{9},\frac{4}{7},\frac{3}{5},\frac{6}{11}$ and $\frac{13}{21}$, which ...
3
votes
1answer
54 views

$\frac{a(a+b)}{4a^2+ab+b^2} + \frac{b(b+c)}{4b^2+bc+c^2} + \frac{c(c+a)}{4c^2+ca+a^2} \leq 1$

I've got stuck at this problem: Let $a$, $b$, $c$ be real numbers. Prove that $$\frac{a(a+b)}{4a^2+ab+b^2} + \frac{b(b+c)}{4b^2+bc+c^2} + \frac{c(c+a)}{4c^2+ca+a^2} \leq 1$$ Firstly, I've ...
3
votes
6answers
200 views

What is the value of $\frac{\sin x}x$ at $x=0$?

On plotting graph for $\frac{\sin x}{x}$ using Wolfram|Alpha and Google, got that : also, I can get the value of $\lim_{x\rightarrow 0} \frac{\sin x}{x} = 1$ using squeeze theorem and as illustrated ...
1
vote
1answer
33 views

How to derive this simple equality?

Let us define $L_i\triangleq \log \left( \dfrac{Prob(x_i=+1) }{ Prob(x_i=-1)} \right)$ $E\{x_i\} \triangleq Prob(x_i=+1)-Prob(x_i=-1)$ I need to show that \begin{equation} E\{x_i\} = ...
2
votes
4answers
143 views

How come $\left(\frac{n+1}{n-1}\right)^n = \left(1+\frac{2}{n-1}\right)^n$?

I'm looking at one of my professor's calculus slides and in one of his proofs he uses the identity: $\left(\frac{n+1}{n-1}\right)^n = \left(1+\frac{2}{n-1}\right)^n$ Except I don't see why that's ...
-5
votes
1answer
54 views

Can't calculate math problem [closed]

Can anyone help me with this math problem? I would require step how you came to the result.
10
votes
1answer
79 views

Prove that $abc$ is a cube of some integer.

Given three integers $a$, $b$ and $c$ such that $\frac{a}{b}+\frac{b}{c}+\frac{c}{a}$ is an integer too, prove that the product $abc$ is a cube. By the way: Merry Christmas! ;)
1
vote
4answers
77 views

What is the simplest way to find $\frac{n}{7}th$ of a line with mathematical proof?

I'd like to know if it is possible to find out the simplest way to get $\frac{1}{7}$, $\frac{2}{7}$, $\frac{3}{7}$, $\frac{4}{7}$, $\frac{5}{7}$ and $\frac{6}{7}$ of a line in 2-dimensional geometry. ...
2
votes
3answers
53 views

How is this limit being solved? I can't grasp it

I am going over limits for my finals as I notice this example in my schoolbook discribing limits of the undefined form $0\over0$ in the shape of an irrational fraction. $$\lim\limits_{x \to 1} ...
251
votes
14answers
30k views

Find five positive integers whose reciprocals sum to $1$

Find a positive integer solution $(x,y,z,a,b)$ for which $$\frac{1}{x}+ \frac{1}{y} + \frac{1}{z} + \frac{1}{a} + \frac{1}{b} = 1\;.$$ Is your answer the only solution? If so, show why. I was ...
0
votes
1answer
22 views

Factors that Impact a Weighted Average the Most

I am trying to determine how to calculate the factors that have the most significant impact on a weighted average. For example, let's say I am reviewing the number of patients that responded to a ...