Twice A Number

What does the phrase "Twice a number x" mean? Why do we replace numbers with letters/symbols?

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mathsworkmusic's profile pic

mathsworkmusic | (Level 2) Educator

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The number "x" is represented as a letter because it is a variable. This is the idea of the type of math that is named algebra. Replacing the variables with single letters (sometimes English alphabet, sometimes Greek alphabet - because the Greeks had a big role in inventing algebra, so we still use their alphabet today) is a shorthand. When we work with long or complicated expressions involving one or more variables, this shorthand makes it easier to follow through the steps on paper at a glance, concentrating it down to the real essentials. It also saves on ink and time!

An example of a variable that "x" might represent is the number of oranges a boy called Sam eats in a week. If his friend Jenny always eats twice as many oranges in a week as Sam, then we can say that she eats "2x" oranges in a week. It is a variable because it varies each week, but the relationship between what the two friends eat always stays the same. You can see that "x" is a shorthand way of saying "number of oranges eaten per week". It is like when you write $ to mean United States Dollars. It makes comparing prices at a glance easier.

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embizze | High School Teacher | (Level 1) Educator Emeritus

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Translate the written/verbal expression "twice a number x" into mathematical/symbolic notation:

Twice a quantity usually indicates to take two of the things in question; usually this indicates to multiply by 2.

Thus "twice a number x" can be written symbolically as 2x.

If this is part of a problem, say twice a number x is 6, then we can rewrite algebraically as 2x=6; dividing both sides by 2 yields x=3. And we can see that, indeed, twice the number 3 is 6 as required. In the expression "twice a number x is 6" twice indicates to multiply by 2, the multiplicand (the thing multiplied by the multiplier 2) is x, and the word "is" can be expressed by the equals sign.

Sources:
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rachellopez | Student, Grade 12 | (Level 1) Valedictorian

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I'm assuming by "twice the number x" that this refers to the numerical equation 2x. When a word problem states that something is twice or two times a number, all it is saying is to multiply your number/variable by 2.

Variables are used for numbers that are unknown. Usually, your goal is to solve for the variable in order to get what number the variable is replacing. For example, if a problem states that "twice the number x equals 14" you could write that as 2x=14. From there, all you do is divide by 2 to get x by itself, making the variable x equal 7. This is a simple algebraic equation that is often used.

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Wiggin42 | Student, Undergraduate | (Level 2) Valedictorian

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You want to translate the phrase " twice a number x " into symbols. Twice means two times. So what you have here is " two times a number " and that number is called " x " . Therefore you can write it as: `2 xx x` . However, its commonly written simply as `2x` . We write phrases in symbols to make computation easier. 

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steamgirl | Student, College Junior | (Level 1) Honors

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Twice the number x means 2 times x or 2x, x being a variable that changes based on the data. Variables are necessary to show that that particular number is not set in stone, and depends on another variable or constant. 

For example, lets say you want to know how many watermelon you have sold at the end of the day, this being represented by y because you don't know what this number is yet. To find this total you must know first, how many crates of watermelon that you have, and secondly, how many are in each crate. The manager tells you that there are 2 watermelon for each crate ( which is the same as saying twice the number x since we don't have the number of crates yet). Knowing that, the number of watermelons you sold is now depends on only the number of crates you sell a day, which could change, not only by the day, but by the hour as well. This leads us into the land of functions, this problem can be represented as y = 2x, and can be graph to visually show your sales.

In summation, we use letters and symbols for numbers that are codependent on some other variable, or are otherwise not set in stone. 

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atyourservice | Student, Grade 11 | (Level 3) Valedictorian

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What does the phrase "Twice a number x" mean? Why do we replace numbers with letters/symbols?

a number = x and the twive usually means you multiply that number (x) by 2
meaning twice a number x is the same as 2x
 
The reason you replace numbers with letters/symbols is because it tells you that number is unknown (think of an x-file) and therefore by putting that symbol we know we have to solve to get that number.
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taangerine | Student, Grade 12 | (Level 1) Valedictorian

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Twice a number x simply means '2x.' Twice means 2 and a number x represents the variable. In this case, they mean multiplication because twice of something means two times. And, this gives us two times x, or '2x'. 

We replace numbers with letters and symbols to isolate the given variable easier. We can differentiate the letter/symbol easier than the numbers, which will make the equation easier to solve with less confusion. 

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maria-vivanco | Student, Grade 11 | (Level 1) Valedictorian

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We use variables to show an equation in order to solve for x. If an expression it's to show a function that x can represent any number

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acompanioninthetardis | Student, Undergraduate | (Level 1) Valedictorian

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Twice a number x" means 2X or 2 of x, which is the same as 2*x

we substitute letters or variables for numbers we do not know.

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zumba96 | Student, Grade 11 | (Level 3) Valedictorian

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Translate the written into a symbol. Twice is equal to 2 and x would be the variable so it would be 2 times the number, therefore the phrase would be 2x, 2 symbolizes the times and x representing the number. This way it is mathematically correct and serves in an equation instead of words. 

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