Lesson 11 Section 3
Three Properties of Division
Dividend ÷ Divisor = Quotient
(The division bar.)
We will explain below why that is true .
This property expresses the fact that multiplication and division are inverse operations.
On dividing the dividend and divisor by the same number:
We see, then, that when the dividend and divisor end in the same number of 0's, we may ignore them, and divide the numbers that remain.
We will now see how to apply Property 2 when the divisor is a decimal. Because the divisor may not be a decimal. The divisor must be a whole number
Example 2. The divisor a decimal. How many times is .2 contained
The divisor must be a whole number.
This example illustrates that, even though we say we are dividing decimals, we can really divide only whole numbers, and then correctly place the decimal point. We will see that again in Lesson 13.
Why did we multiply by 100? Because that makes the divisor .03 into the whole number 3.
In other words:
If the divisor is a decimal, multiply it by 10, or 100,
on dividing 12 by 2.
on dividing 8 by 2.
Or, finally, on multiplying first:
These three possibilities imply:
When division is signified by the division bar, then the order
Also, if we decompose the dividend into factors, then we can sometimes find a multiple of the divisor.
For the explanation why Property 3 is true, see below.
Explanation of the properties of division
Arithmetic is the first science. We look at facts themselves. We will explain the properties of division by looking at the arithmetical meanings of multiplication and division, and the relationship between them. This is not algebra.
To illustrate that, let us start with 5, and then multiply it by 3:
3 × 5
And now, let us divide by 3. Let us repeatedly subtract 3's. But since 15 is now composed of 5's, how can we do that?
According to the order property of multiplication,
3 × 5 = 5 × 3.
And so the product is made up of 3's -- it is made up of five 3's.
15 ÷ 3 = 5.
Hence we are back where we started, at 5.
The student should realize that the multiplication table -- 3 × 5 = 15 -- is not the point here. The point is to understand -- to see -- that while 3 × 5 is a sum of 5's, we can still subtract 3's.
This property, after all, holds for any numbers.
(206 × 19) ÷ 19 = 206.
Understanding that has nothing to do with knowing the "answer" to 206 × 19
Next, let us start with 15 and divide it by 5:
We will get 3, because
3 × 5 = 15.
But according to the order property,
5 × 3 = 15.
Therefore, if we now multiply 3 by 5, we will get back to 15
The quotient is the number of times the divisor is contained in the dividend.
As many times, then, as we increase or decrease the dividend -- and keep the divisor the same -- the quotient will increase or decrease that same number of times.
If we double the dividend, the divisor will go in twice as many times, that is, the quotient will double. If we triple the dividend, the quotient will triple.
On the other hand, if we divide the dividend by 2, that is, is we take half of it --
-- then quotient will also be half. And so on.
Next, as many times as we increase or decrease the divisor -- and keep the dividend the same -- the quotient will decrease or increase that same number of times.
If we double the divisor, the quotient will be half. If we triple the divisor, the quotient will be one third as much.
-- it will go in twice as many times. If we divide the divisor by 3, the quotient will triple. And so on.
Therefore, if we increase or decrease the dividend and the divisor the same number of times, the quotient will not change.
In other words: The quotient will not change if we multiply the dividend and divisor by the same number, or if we divide them both by the same number.
(3 × 20) ÷ 5 = 3 × (20 ÷ 5)
That is, to divide 3 × 20 by 5, we may first divide 5 into 20, and then multiply by 3.
Here is (3 × 20) ÷ 5 -- Three 20's divided by 5:
But that is the same as (20 ÷ 5) --
-- added three times! Therefore,
(3 × 20) ÷ 5 = 3 × (20 ÷ 5).
Please "turn" the page and do some Problems.
Continue on to the next Lesson.
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Copyright © 2012 Lawrence Spector
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