I used to LOVE this duet when I heard it at music festivals as a kid. Found it in the digitrad - sorry I don't know how to link you there directly yet but here goes ...Not exactly folk, but what the heck:

ANYTHING YOU CAN DO, I CAN DO BETTER
(Irving Berlin)

I'm superior, you're inferior
I'm the big attraction, you're the small.
I'm the major one, you're the minor one
I can beat you shootin', that's not all

Anything you can do, I can do better
I can do any thing better than you
No you can't. Yes I can. No you can't.
Yes I can. No you can't. Yes I can, yes I can.

Anything you can be I can be greater
Sooner or later, I'm greater than you
No, you're not. Yes I am. No you're not.
Yes I am. No you're not. Yes I am, yes I am.

I can shoot a partridge with a single cartridge
I can get a sparrow with a bow and arrow
I can do most anything
Can you bake a pie? No. Neither can I.

Anything you can sing I can sing louder
I can sing anything louder than you
No you can't....

Anything you can buy, I can buy cheaper
I can buy anything cheaper than you
Fifty cents. Forty cents. Thirty cents.
Twenty cents. No you can't. Yes I can, yes I can

Anything you can dig, I can dig deeper
I can dig anything deeper than you
Thirty feet. Forty feet. Fifty feet.
Sixty feet. No you can't. Yes I can, yes I can

I can drink my liquor faster than a flicker
I can do it quicker and get even sicker
I can live on bread and cheese
And only on that? Yes. So can a rat.

Anything you can reach, I can go higher
I can sing anything higher than you
No you can't....

Anyone you can lick, I can lick faster
I can lick anyone faster than you
With your fist? With my feet. With your feet?
With an axe. No you can't. Yes I can, yes I can

Any school where you went, I could be master
I could be master much faster than you
Can you spell. No I can't. Can you add.
No I can't. Can you teach. Yes I can, yes I can

I could be a racer, quite a steeple chaser
I can jump a hurdle even with my girdle
I can open any safe.
With out being caught? Yes. That's what I thought, you crook

Any note you can hold I can hold longer.
I can hold any note longer than you.
No you can't. Yes I ca-a-a-a-an. Yes you ca-a-an