Number is the symbol for a known quantity

Variable is the symbol for an unknown quantity

Amount is the extent of something

Value is a known numerical amount

Quantity is a known or unknown numerical amount

In other words, a quantity is always a value, but a value is not necessarily a quantity. Take for example the variable, which is a quantity that can have different values.

]]>Ricky once proved that lots of definitions in dictionaries eventually were circular. It led me to distrust them, especially when dealing with math definitions.

Wiki wrote:

]]>A number is a mathematical object used to count, label, and measure.

I don't really understand the definition of a number: Is it safe to say that it's an abstract quantity?

]]>What is a number then? What's the difference between quantity and number?]]>

I would use 'value' in equations and formula such as

What value of x makes this equation true ... 2x + 3 = 17 ?

If F = 9C/5 + 32 ... what is the value of F if the value of C = 40 ?

I would use 'quantity' when measuring something such as

What quantity of sand is needed to make a 3:1 concrete mix if I have 25 kilos of cement.

I think you can always change 'what quantity of' to 'how much'; thus

How much sand is needed .......................?

EDIT: I've just looked on dictionary.com and found this:

value 6. maths

a. a particular magnitude, number, or amount: the value of the variable was 7

b. the particular quantity that is the result of applying a function or operation for some given argument: the value of the function for x=3 was 9

Interesting that they use the word quantity whilst defining value.

quantity

4. Mathematics .

a.

the property of magnitude involving comparability with other magnitudes.b.

something having magnitude, or size, extent, amount, or the like.c.

magnitude, size, volume, area, or length.

So perhaps the main difference is that value is used when you want to be specific, such as

I have a number of piles of objects. I know the quantity of objects in each pile. Which value will satisfy this specific requirement ..............

Bob

]]>What's the difference between "value" and "quantity"?

Thanks for help.

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