Mathematics Stack Exchange
Mathematics Stack Exchange

Questions tagged [arithmetic]

Questions on basic arithmetic involving numerical quantities only. Questions involving variable values (other than the result of the operation) should be placed under the (algebra-precalculus) tag. Questions about number theory (sometimes called "arithmetic") should not use this tag and should instead use (number-theory) or (elementary-number-theory).

Arithmetic is defined as operations upon numbers using $4$ main operations along with many others:

addition - the sum of two numbers

subtraction - the difference of two numbers also defined as the addition of negative numbers

multiplication - the area of a rectangle with sides of lengths equal to the two operands

division - the number of times one number can be subtracted from another before equaling zero. Sometimes it will allow decimals and in other cases there will be a remainder left over when a number doesn't go into another evenly

See Arithmetic.

6283 questions
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Closure -- why does it matter?

I understand the concept of a set having closure under a particular operation; that, for example, the natural numbers are not closed under subtraction. But why does closure matter? Is it necessary for an operation to be closed to be useful? If…
Thurber
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product of 3 numbers from a set of 7 numbers

Set $S$ consists of the integers from -1 to 5, inclusive. If $N$ is the product of three distinct members of Set $S$, how many unique values of $N$ are there? I thought of it like this--> there are $7$ numbers so if we multiply by any $3$ out of it…
atir
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Confused about $(-1) \times (-1) = (+1)$

Why the product of two negative numbers is a positive number? We all learn about it, and I'm not sure why it is like that. Is it a convention or what?
Johnny Bre
  • 159
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4 answers

What is my grade percentage

If I get 45 percent on an assignment worth 85 % and 45 percent in an assignment worth 15% what is my final grade. or otherwise worded as I have 2 assignments one worth 85% the other worth 15% what is my final grade if i get 45 percent on the both?
sammy
  • 11
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How far does she travel in her Journey?

Ok, I'm doing a Mock End of Unit Test Revision paper and I'm stuck on a few questions. The first question is: Susan completes the journey in $2$ stages of her journey. In stage 1 of her journey, she drives at an average speed of $80$km/h and takes…
user61406
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Why is dividing by zero = undefine.

I know that $ a\cdot\left(\frac1a\right)=1$ as long as $a$ is not $= 0$, but when we divide $(\frac a0)$ is $=$ we say it's undefined. why is it really undefined? what's the big conspiracy here.
Ahmad Khan
  • 137
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Converting distance and time to pace

I am trying to work out pace by doing time / distance. So for example if I run for for 39 minutes and cover 5 miles it gives me 39 / 5 = 7.8 This is correct but I want to result to be in minutes and seconds rather than a decimal. So what I…
Pattle
  • 123
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How to figure percentage change?

How would I figure out the percent a number change has? Let's say I have this number: 88 and now it's 240. How would I find out the percent raise it went up by? Thanks.
test
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Dividing x by (1+x) the unusual way

Why this way of dision is not correct; that is, changing the order of the terms of divisor as and when required? Even though $1+x$ is same as $x+1$ Check: (quotient)X(divisor)+(remainder) gives$[(1-1+1-1)(1+x)]+x=x$ Same thing happens when we…
Vikram
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Adding weightage to number.

I have four numbers x=50 y=30 z=20 sum of x+y+z=100 if i want to add a number n where n=(x+y)/2 Edit: n=45 such that x+y+z+n=100 now x+y+z=100.If any number (45 here) is added, then the sum should be always 100. i.e we need to subtract…
Madhav Bhattarai
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Elementary rounding

Mr. Brown rounded $14.486$ to the nearest whole number by rounding $14.486$ to $14.49$ by the "over $5$" rule. Then he rounded $14.49$ to $14.5$ by the same rule. Then he rounded $14.5$ to $15$ by the rule. Unfortunately this is wrong. Why is his…
Suzanne collier
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How to justify the rule for the product of square roots of real numbers?

Why $\sqrt{a}$ * $\sqrt{b}$ = $\sqrt{ab}$ ? It's easy to verify that it works in some cases, like in $\sqrt{4}$ * $\sqrt{9}$ = $\sqrt{36}$. But why does the general rule work?
João Rimu
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Setting up a word problem.

I cannot figure out if this is right because there is no example to verify calculations and I have gone over this a few hours now. I do not need help with programming, just the correct mathematics. "Your kid brother plans to start a lawn-mowing…
Hermes Trismegistus
  • 429
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Could someone please help me understand this question?

I was given this question today as part of a technical analysis, which I failed to answer. I am not sure what is expected? Is it really just a case of substituting the values at the bottom in place of ...? It seems unlikely. Can someone please…
JL.
  • 139
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A couple of problems on set theoretic manipulations and / or percentages

Problem 1: A public opinion poll shows that 93% of the people agree with the government on the first decision, 84% on the second, and 77% on the third, for the three decisions made by the government. At least what percentage of the population in…
Saaqib Mahmood
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