Why does flipping the second fraction around and then multiplying work when dividing two fractions?

305 views

Eg. 8 over 3 divided by 1 over 3 = 8 over 3 times 3 over 1

In: 13

6 Answers

Anonymous 0 Comments

Division is the opposite of multiplication.

So dividing by a dividing thing is a double-division, so the opposite of the opposite of multiplication; which is just multiplication.

Because division and multiplication are the same kind of thing(ish), we can always do them in any order. So:

> 8/3 divided by 1/3

can be split up into:

> 8 divide by 3, divide by 1, divide by “divide by 3”

but that “divide by divide by 3” is a double division, so a multiplication:

> 8 divide by 3, divide by 1, multiply by 3

We can now re-order that:

> 8 divide by 3, multiply by 3, divide by 1

and then join these bits up together again to get:

> 8/3 multiply by 3/1

It is a deceptively complicated process but it only relies on division being the opposite of multiplication, and that you can re-order (and regroup) division and multiplication.

And understanding that fractions are the same as division.

[This also means that phrasing and brackets are important. 8/1/3 could be “8 divide by 1, divide by 3”, or it could be “8 divide by (1 divided by 3)” (so 8 multiplied by 3). ]

You are viewing 1 out of 6 answers, click here to view all answers.