Math representation of the compound rule of three

Off-Topic
1

Hi
The basic rule of 3 is represented by this equation a/b=a2/b2
For example if 2 apples cost 3dollars, how many apples can I get with 5$ ? —>> 2/3=x/5

In case of the compound rule of three, this should be the equation a/b/c=a2/b2/c2
Is this always right ? Or is it right depending on inverse/direct proportionality between a,b and c?

Thanks

2

Googled the following, hope it helps (I’m terrible at maths)

http://www.emathzone.com/tutorials/everyday-math/compound-proportion.html

3

That’s expensive apples.

And you’ll get three apples (as I haven’t met a grocer yet willing to sell bits of apple) :wink:

And I would say the proportionality is important: it takes 2 men 4 days to build a wall. How long does it take 8 men? 16 days?

4

Thanks Julian
I googled it before asking here but I didnt find that page that you linked wich is the best so far.