I should guess the weight of the rock at the Bicycle Shop.

I saw that as I was driving by the other day, and then I saw it again just now when they had an ad on Facebook.

How to guess the weight of the rock:

1. Take a photo, or use your photographic memory, to get an image of the rock's colors and patterns. Then go to somewhere on the net, some geology site, and look at photos of rock types. Try to identify what type of rock it probably is (quartz, etc). Then look up the DENSITY of that type of rock. This won't be exact, but it will be a general idea. You would have to use the same UNITS OF MEASUREMENT that were used in the density given to you. I don't know what those would be.

2. I haven't been close enough to get a good look at the rock's shape. However, it looks like it's a nice, neat, regular, geometric shape. That makes everything much easier. It isn't just a random lumpy rock.

It's almost a rectangle on one face, and some kind of triangle on another face. I think the other face is a rectangle too. You want to find the rock's VOLUME. Finding the volume of a regular, neat-and-tidy, geometric shape is something you can do using relatively simple math. (I say 'relatively simple' because I haven't actually tried to do it, and it might be one of those things where if I tried it, I'd discover that I forgot about a bunch of important things that would make it actually a hassle.)

Find the area of each face of the rock.

Rectangular Faces: Measure the length and width of the rectangle. Multiply the length times the width.

Semi-Triangular Face: The top face, that the bike is sitting on, is sort of triangular. I haven't gotten close enough to really see. It might be rounded, almost like the arc of a circle. That looks like the hardest one to find the area of.

You'd have to find some 'name' to call that shape. Is it a triangle? What type of triangle? It isn't an equilateral triangle, and it isn't an isosceles triangle. It might possibly be 'scalene' (a 'none of the above' type of triangle). Looking at the picture I see that it might even have four sides, not three, so it might be a quadrilateral. I'm looking at a web page now, http://www.mathleague.com/help/geometry/polygons.htm, and reading the names, because it's been a couple decades since I took geometry class. (Almost that long. Wow. Was I fifteen? Sixteen?)

So, after you've figured out what name to call it, you look up the formula for the area of that shape. I vaguely remember how to find the areas of strange shapes, but I can't really explain it. It's something that I sort of figure out as I go, because some secret part of my brain knows what to do, but can't put it into words. (It's one of those right-brained things.)

Well, the general idea is 'Multiply everything together.' I mean, multiply the areas of all those sides that you found. However, actually, that's wrong... Don't do that. I don't know how many sides it has, and it isn't really rectangular. You could do it if it were only a rectangle.

You might have to do something more complicated. You might have to subtract the shape from an imaginary shape. Like, an imaginary rectangular solid object. I don't know for sure.

The details are unimportant!

Maybe I should just go try to do it.

No, no, no. Multiply the "weird side's" area times the rock's height. That's all. Find the area of the strange shaped face that the bike is sitting on (the triangle-like or quadrilateral thing), then multiply that area times the rock's height. The top and bottom surfaces of the rock are flat, not angled, so it's okay to do that. It could potentially be really complicated, but it isn't. Nothing is angled. Everything goes straight down, and everything is flat, from what I've seen of the rock. (I should go look.)

3. After getting the volume, and also having the suspected density of the suspected type of rock it is, you can find the weight. Fill in the variables in the density equation. It's something like Density=Weight/Volume.

I used to enjoy geometry class.