> Start from deep points TOP> What is 1 as ratio?
1. What is 1 as ratio?
THAT IS,
a standard unit size of discussed matters there.
(Weight and length also are measured as big or small,
because we think them as numbers.
So we can describe them as size.)
I set my length (I hope you to read 
as you.) as 120 cm now.
And I assume "My length" as the standard length of this world, .
Then "My length" means 1 (in circle, "I" is there, not "1 (one)").
Here, my father's length is 180 cm.
180=120x1.5
Then "My father's length"=1.5x "My length."
So "My father's length" is 1.5 times of "My length" as the standard length of this world.
So "My father's length" turns 1.5.
In ratio,
we omit from this 1.5 representation of my father's length.
(To whatever in this world, is the standard in this discussion.
So we can decode to that original size and understand it,
even if we omit , the origin of the standard.)
That is, my father's length is 1.5 (15 hundred) of my length in ratio.
And now, in the previous calculation,
if we exchange into "1",
a number "1.5" does not change.
So when we make the standard as 1,
results of multiplications are straightly another number of product.
So it is convenient for us to make standard as 1 rather than other numbers.
When we solve quizzes,
we are usually said "when we want to get a ratio, we must divide."
Let's think a quiz.
For example,
"a cost price of your item is 800 dollars, and a catalog price of it is 1000 dollars.
Then how much ratio of a catalog price is a cost price?"
In this quiz, we are asked "how much ratio of a catalog price" here.
So the standard of this quiz is "a catalog price."
Here, we can think a price of everything (including a profit and a discount and so on)
as how much times of a catalog price.
In this question,
we are asked, "a cost price is how much times of a catalog price."
I show this sentence in a equation,
800=
x1000
So we are asked of this equation.
Then we calculate as 800 / 1000 =0.8.
The answer is,
"A cost price is 0.8 of a catalog price."
A ratio is 0.8.
(I omitted what is a standard,
that is, a catalog price.)
Sometimes even in one quiz,
standards change.
But to make our confusions lesser,
we must neatly check one by one what is a standard now.
