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

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1
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2answers
22 views

Simplification of rational expressions

I have the following expression: $${2\over x-2} + {2 \over{x^2} -5x +6}$$ So I can simplify this as: $${2 \over x -2} + {2 \over (x -3) (x-2)}$$ I make the common denominator to be ${(x-3)(x-2)}$ ...
0
votes
1answer
19 views

Trending proof for fairly simple fraction

(Please humour the physicist!) Why does $\left(\frac{1-a}{1-a^b}\right) \to \frac{1}{b}$ as $a \to 1$? This came from a calculation involving flow measurement of gases, and although I can see and ...
1
vote
2answers
35 views

Exponential function negative: $\left(\frac{81}{4}\right)^{1/4}\left(\frac{1}4\right)^{-3/4}$

This is another example. $\left(\dfrac{81}{4}\right)^{1/4}\left(\dfrac{1}4\right)^{-3/4}$ Multiply on both sides equals $\dfrac{81^{1/4}}{4^{1/4}}\cdot \dfrac{1^{-3/4}}{4^{-3/4}}$ This should be ...
-1
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2answers
65 views

How to show $\frac12\cdot\frac34\cdot\frac56\cdots\frac{99}{100}<\frac{1}{12}$? [on hold]

How can I show that $$\frac12\cdot\frac34\cdot\frac56\cdots\frac{99}{100}<\frac{1}{12}?$$
0
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4answers
28 views

Simplifying a fraction with a cubed root in the denominator

I have an equation the following equation in my textbook, but I don't understand how it's legal for it to be simplified this way. $${1000\over \pi\sqrt[3]{500\over \pi}^2}=2\sqrt[3]{500\over \pi}$$ ...
0
votes
1answer
114 views

Four mathematical notations for fraction $1/999$ and how to show/present they are equal

I need some help for notation. I need to present fractions in four different format and I'd like to get it right. I just take $1/999$ for example, but of course it could be any fraction with positive ...
2
votes
5answers
82 views

The expression $(1+q)(1+q^2)(1+q^4)(1+q^8)(1+q^{16})(1+q^{32})(1+q^{64})$ where $q\ne 1$, equals

The expression $(1+q)(1+q^2)(1+q^4)(1+q^8)(1+q^{16})(1+q^{32})(1+q^{64})$ where $q\ne 1$, equals (A) $\frac{1-q^{128}}{1-q}$ (B) $\frac{1-q^{64}}{1-q}$ (C) $\frac{1-q^{2^{1+2+\dots +6}}}{1-q}$ ...
-8
votes
4answers
61 views

how to multiply a fraction [closed]

$$\frac{7}{12} \times \frac{8}{21}$$ ...
2
votes
5answers
81 views

If $\frac{a+b}{b+c}=\frac{c+d}{d+a}$ then..

If $\frac{a+b}{b+c}=\frac{c+d}{d+a}$ then (A) $a=c$ (B) either $a=c$ or $a+b+c+d=0$ (C) $a+b+c+d=0$ (D) $a=c$ and $b=d$ I solved $\frac{a+b}{b+c}=\frac{c+d}{d+a}$ and got $a(a+b+d)=c(c+b+d)$ and ...
8
votes
1answer
471 views

Primes and certain unit fractions [closed]

Are there primes $p,q$ and a natural number $a$ such that $\frac{1}{p}+\frac{1}{q}=\frac{1}{a}$?
0
votes
1answer
29 views

Can $\dfrac{b_0}{a_0} + \dfrac{b_1}{a_1} + \dfrac{b_2}{a_2} + \dfrac{b_3}{a_3} + … + \dfrac{b_n}{a_n}$ be represented as …

Is this correct? (Last step $\rightarrow$ After taking L.C.M.) $\large \dfrac{b_0}{a_0} + \dfrac{b_1}{a_1} + \dfrac{b_2}{a_2} + \dfrac{b_3}{a_3} + ... + \dfrac{b_n}{a_n} = \sum\limits_{k=0}^{n} ...
6
votes
1answer
62 views

Certain Fraction between Fractions

Is there always a fraction $\frac{r}{s}$ with $\frac{p}{q}<\frac{r}{s}<\frac{p+1}{q}$ and $s<q$ for $0<p<q-1\in\mathbb{Z}$ and $r,s\in\mathbb{Z}$?
0
votes
0answers
39 views

how to divide a whole by 2 unequal fractions [closed]

An estate valued at $310,000$ is liquidated and the money is split to seven people. One person receives $1/6$ and the remaining $6$ get $1/7$ how do you do the math.
0
votes
1answer
40 views

Convergent conjecture: What is the proof?

Lets say that $\def\nn{\mathbb{N}}$$\def\rr{\mathbb{R}}$$K : \nn \to \rr$ and $\displaystyle \sum_{i=1}^\infty \frac{K(i)}{K(i+1)}$ is a convergent sum. My conjecture is that the function $K$ must be ...
0
votes
1answer
33 views

Choosing suits of cards in a row

Three cards from a standard deck are dealt. What is the probability that the first is a heart, the second is a spade, and the third is another heart? I have figured out so far that you can use ...
1
vote
3answers
61 views

Mathematical Induction getting the right side

So I 've been doing Mathematical Inductions but I seem to have a issue in simplify and getting the right side. So I have this on the L.H.S $$\frac{k(k + 1)(2k +1)}{6} + (k + 1)^2 $$ And I'm trying ...
1
vote
2answers
31 views

Expression for binomial coefficient denominator

I'm trying to find an analytical expression for the denominator of $\pmatrix{-1/2\\k}$ in terms of $k$ when the fraction is fully reduced. E.g., the first several such denominators, starting with ...
0
votes
1answer
30 views

How to calculate $n$th term in terms of constants?

The expression is $$\large t_n=\frac{(x\times t_{n-1})^2}{((x-t_{n-1}\times y)^2+4\times x\times t_{n-1})\times t_{n-2}}$$ where $x$ and $y$ are constants. $t_0$ , $t_1$ , $t_2$ , $t_3$ and $t_4$ ...
2
votes
1answer
31 views

Congruence of 2 fractions—how to properly rewrite in terms without modulo?

EDIT: Following Theo's comment, the equivalence holds since one can (must) rewrite $1/a$ as $(1+23k)/a$. Provided that $$\frac{1}{25} \equiv \frac{1}{2}\pmod {23}$$ is true, why can I not rewrite ...
7
votes
1answer
99 views

Distribution of the sum reciprocal of primes $\le 1$

$$\frac{1}{2}+\frac{1}{3}+\frac{1}{7}+\frac{1}{43}+\cdots \le 1 $$ This is an interesting infinite summation. This is very closely resembling my other problem with has to do with the distribution of ...
7
votes
2answers
104 views

Does the sum of the reciprocals of composites that are $ \le $ 1

The sum itself: $$ \frac{1}{4}+\frac{1}{6}+\frac{1}{8}+\frac{1}{9}+\frac{1}{10}+\frac{1}{12}+\frac{1}{14}+ \frac{1}{15}+ \frac{1}{39}... \le 1 $$ These are all sums of reciprocals of composites that ...
-1
votes
2answers
69 views

Find all integer numbers $n$ such that $\frac{11n-5}{n+4}$ is a perfect square.

Find all integer numbers $n$, such that, $$\sqrt{\frac{11n-5}{n+4}}\in \mathbb{N}$$ I really tried but I couldn't guys, help please.
0
votes
0answers
42 views

Can This Expression Be Simplified? (Involves Square Roots)

I started with the expression $$ \frac{4mlt(1-\sqrt{1-\frac{v^2}{c^2}})c^2}{\sqrt{1-\frac{v^2}{c^2}}} $$ and have ended up at: $$ \frac{4mlt(c^2 - c \sqrt{c^2-v^2})}{\sqrt{1-\frac{v^2}{c^2}}} $$ ...
0
votes
3answers
77 views

Problem with simplifying $\frac{(3+h)^2-9}{(3+h)-3}$ [closed]

I need help simplifying $$ {(3+h)^2-9\over (3+h)-3}. $$ The answer is $6+h$. I keep getting $h$.
0
votes
2answers
48 views

How can I approximate a decimal with two fractions where denominator is less or equal to $d$

I was looking for a way to approximate a decimal number with a fraction, whose denominator is less or equal to $d$. Basically, having a decimal $X$, I want to find two fractions such that ...
62
votes
14answers
11k views

Express 99 2/3% as a fraction? No calculator

My 9-year-old daughter is stuck on this question and normally I can help her, but I am also stuck on this! I have looked everywhere to find out how to do this but to no avail so any help/guidance is ...
2
votes
1answer
41 views

How to simplify a diabolical expression involving radicals

A friend and I have been working on this problem for hours - how can the following expression be simplified analytically? It equals $\frac{1}{2},$ and we have tried the following to no avail: ...
2
votes
1answer
43 views

When we can change the sign of denominator

Suppose $z=\frac{-x_1}{x_2-x_3}$, find $-z$. Which one is correct $$-z=\frac{x_1}{x_2-x_3}\ \ \ \text{or}\ \ \ -z=\frac{x_1}{-x_2+x_3}$$
3
votes
2answers
36 views

SAT math problem about solute and solution

There are two solutions $P$ and $Q$. There are $50 g$ of $P$, which has $30\%$ benzene by mass, and $200 g$ of $Q$, which has $70\%$ benzene by mass. If $20 g$ of solution $P$ is added to $20 g$ of ...
4
votes
3answers
150 views

Why does $\frac{49}{64}\cos^2 \theta + \cos^2 \theta$ equal $\frac{113}{64}\cos^2 \theta $?

I have an example: $$ \frac{49}{64}\cos^2 \theta + \cos^2 \theta = 1 $$ Then what happens next: $$ \frac{113}{64}\cos^2 \theta = 1 $$ Where has the other cosine disappeared to? What operation ...
2
votes
2answers
37 views

decimal to fractions

When being asked how to solve the Arithmetic Means of 8, 7, 7, 5, 3, 2, and 2, I understand that adding these numbers then dividing by 7 (the amount of numbers) gives me the decimal 4.85714... But ...
39
votes
0answers
2k views

If the decimal expansion of $a/b$ contains “$7143$” then $b>1250$

I recently stumbled upon this really interesting problem: If we have a fraction $\frac{a}{b}$ where $a,b \in \mathbb{N}$ and we know that the decimal fraction of $\frac{a}{b}$ has the numerical ...
2
votes
2answers
79 views

Here are two fractions, $\frac{2}{3}$,$\frac{7}{8}$, which of these fractions are closer to $\frac{3}{4}$?

I've been throwing this question around my family. No one has a clue, therefore can someone help? I'm pretty sure this will be easy to do
2
votes
3answers
102 views

Get rid of the square roots of the denominator: $\dfrac{1}{\sqrt{7}-2\sqrt{5}+\sqrt{3}}$

How to get rid of the square roots of the denominator: $\dfrac{1}{\sqrt{7}-2\sqrt{5}+\sqrt{3}}$? I squared the whole denominator, but that didn't help. Also I searched for a propriety or ...
0
votes
2answers
68 views

Fractions of an amount [closed]

I need help with the following problem: Catalin works in an office. One week he divides his time between these tasks: $\frac{1}{4}$ of his time in meetings $\frac{5}{8}$ of his time writing ...
2
votes
1answer
75 views

Are fractions with zero divisors in the denominator never well defined?

Are fractions with zero divisors in the denominator never well defined? I know that for a fraction in modular arithmetic to be well defined, the denominator must not be a zero divisor, e.g: $$ x ...
0
votes
4answers
86 views

Dividing fractions in real life scenario / application

First of all sorry if this question sounds too stupid or offends anyone. One apple divide by two you get half an apple. $\large{\frac{1}{2} = 0.5}$ I couldn't get my head around with dividing ...
3
votes
4answers
397 views

SAT Maths Question About Fractions

Whilst revising, a problem caught my eye and I cannot seem to find an answer. I am usually bad at these types of questions. On a certain Russian-American committee, $\frac23$ of members are men, ...
0
votes
3answers
81 views

$(5x +1) ÷ (3x)$ is not a polynomial?

On the Mathwarehouse page on polynomial equations, it gives this expression as an antiexample, something that is not a polynomial: $(5x +1) ÷ (3x)$ However, it also says on the same page that if it ...
2
votes
1answer
20 views

Fractions and Largest Common Multiple, Algebra, Numerator and Denominator Identical Numbers?

This is the question find $x$ of equation: $$\frac{5x-2}{5} - \frac{2x+3}{2} = 3$$ I tried multiplying this all by 10, the LCM. It ended with: $x -x=49.$ How do you solve this without cancelling ...
0
votes
5answers
47 views

How does this seemingly-trivial simplification work?

In a section on inductive proofs in the book Modelling Computing Systems: Mathematics for Computer Science (Muller, Struth) there is a simplification that is assumed to be trivial, but that I can't ...
1
vote
1answer
47 views

Can we write “fractional root” symbol in math?

Fractional exponents are legit but I have never seen fractional roots, so I just wonder if we can write fractional roots such as this: It sometimes can be convenient to think about too.
4
votes
6answers
453 views

Is $15/52$ equal to $17/59$?

Is $\frac{15}{52} = \frac{17}{59}$? I typed it into the calculator and found: $$\frac{15}{52} = 0.2884615 $$ $$\frac{17}{59} = 0.2881356 $$ So I thought they were different. But then my friend said ...
0
votes
1answer
25 views

Simplification imaginary fractions

In an exercise, a partial fraction expansion has to be done. I have no problem with that, but one of the last steps includes a simplification as follows: \begin{equation*} \left( -\frac 12 - \frac 16 ...
0
votes
3answers
29 views

Ordering an even and odd fraction that are close

We know that $1/4 < 5/11 < 1/2$. I did it this way from small to large: $$\frac{1 \cdot 3}{4 \cdot 3} = \frac{3}{12}$$ $$\frac{5}{11}$$ $$\frac{1 \cdot 6}{2 \cdot 6} = \frac{6}{12}$$ It is ...
-1
votes
3answers
60 views

How to show simple inequality of fractions

If $$\frac {a}{a+b}<\frac{a'}{a'+b'}$$ then how can I show that $$\frac {a}{a+2b}<\frac{a'}{a'+2b'}\ \forall\ a,b,c>0$$ I tried puitting in a constant k so $$\frac ...
0
votes
1answer
21 views

Farey Sequence implemenatation

I'm trying to use the Farey sequence to get the next lowest reduced fraction in a list. For example, for $n = 8$, we have $\dots, \frac13, \frac38, \frac25, \frac37, \frac12, \dots$ So let's take ...
2
votes
2answers
30 views

Sign of fractional exponent [duplicate]

What is the sign of $-1^{\frac{2}{3}}$? I thought it was positive 1 because it involves squaring, but that doesn't seem to be the case. Why?
1
vote
2answers
51 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 ...
4
votes
4answers
96 views

How does $-\frac{1}{x-2} + \frac{1}{x-3}$ become $\frac{1}{2-x} - \frac{1}{3-x}$

I'm following a solution that is using a partial fraction decomposition, and I get stuck at the point where $-\frac{1}{x-2} + \frac{1}{x-3}$ becomes $\frac{1}{2-x} - \frac{1}{3-x}$ The equations are ...