Need Help From Math Geeks!

[Rick Inman]

OK, get out your coke-bottle glasses and take the slide ruler out of your pocket protector. I need some math help.:22:

I bought one of those cheap above ground pools, and it needs a perfectly level surface under it. Unfortunately, my back yard has a small slope to it that I have to level out with Pea Gravel. Here's the numbers:

I need to level out an 18'X18' square area with the Pea Gravel. I don't know the angle of the slope, just that it slopes down 6". They sell Pea Gravel by the square yard.

So, how many square yards do I need to level out the 18'X18' square area on a slope that slopes down 6"? (Just to be clear, I don't need to raise the entire square 6', but gradually for 0" on one side to 6" on the other. Clear?)

This should be an easy one for all you math geeks who are just sitting at home watching Star Trek re-runs unable to get a date. :clement2:

Thanks!



BTW, I expect Lamont to see this thread when he does his daily search for "Star Trek."

 

[Marek K]

OK Rick, I'll take a stab at it. And I even do have coke-bottle glasses! Though be warned... I did change my major from engineering to international relations, before graduating in, um, 1976.

See attached sketch... I conclude from what you wrote that the 18' x 18' area is on the surface of the slope; that is, the green area? And you're going to excavate down and/or build up to make a flat surface; that is, the grey area? And that the grey area is what you need the area of, to cover in Pea Gravel?

Bottom line up front: The slope is really negligible, compared to the run. You'd be almost exactly right on, assuming a flat 18 ft x 18 ft surface
= 6 yd x 6 yd (conveniently)
= 36 sq yd of Pea Gravel.

One level of detail higher: By my calculations, considering the slope, you'd actually need 35.982 sq yd. But I think the "precision" in that figure is misleading, assuming your original measurements are an approximation. In other words, again, order 36 sq yd.

Yet one level of detail still higher: In the sketch,

(ab)2 + (ab)2 = (eb)2

(ab)2 = (eb)2 - (ab)2

= ( (eb)2 - (ab)2 )2

(ab) = (6.02 - 0.172 )½ yd (converted from feet)

= (36.0 - 0.029)½ yd

= 35.971½ yd

= 5.997 yd


So what you're looking for, area (abcd), = (ab) x (ad)

= 5.997 yd x 6.0 yd

= 35.982 sq yd.

Someone needs to check my logic and algebra. Yes, I realize I'm inconsistent regarding significant places.

If I'm wrong, you see why I changed majors.


(Edit: Okay, why isn't this post accepting superscripts (the 2's and 1/2's, representing squares and square roots)??

--Marek

 

[jonnythan]

Hrm.. the surface is indeed 36 sq yards, but that doesn't say anything about the depth here.

The problem is that I have no idea what thickness the amount "1 sq yd of pea gravel" is meant to fill. For instance, it makes a big difference if that was meant to be 0.5" deep (in which case you'd need 216 'square yards') or 6" deep (in which case you'd need 18 'square yards'). We're not talking about covering a 36 square yard area with gravel, we're talking about filling a volume with gravel and 2-dimensional measurements don't help an awful lot.

You need about 3 cubic yards (81 cubic feet) of gravel, if that helps out somehow.

 

[Charlie99]

I also figure 3 cubic yards.

18'x18' is 6x6yards = 36 square yards.

Average depth is 3" = 3/36= 1/12 yard deep.

36 x 1/12 = 3 cubic yards.

 

[cornfed]

You need about 3 cubic yards (81 cubic feet) of gravel, if that helps out somehow.

Yep.

Rick, on another note... are you sure pea gravel is the best choice? I assume you need a level -compact- surface that won't shift. In my experience, pea gravel shifts a lot.

 

[Marek K]

Um, yeah... I didn't figure in how deep you wanted the gravel to be. I just assumed subconsciously that there was a "standard" depth to the gravel, and that's why you said it was sold by the square yard.

Man, you should know better than to ask even simple questions on ScubaBoard!!

--Marek

 

[cornfed]

Um, yeah...

Do me a favor. If they decide to remodel the Embassy in Warsaw, promise me you won't help the architect.

 

[Marek K]

Do me a favor. If they decide to remodel the Embassy in Warsaw, promise me you won't help the architect.

Where's Pug when you need him?

 

[Marek K]

Actually, it's been a standing joke that the U.S. Embassy here is the second-ugliest in town.

The ugliest has always been the French, just down the street.

The French have just finished completely remodeling their building. And guess what?

We're still the second-ugliest!!

 

[cornfed]

Roflmao