NeoPets Riddles (Lenny Conundrums) and Answers Here

The cross section IS A SQUARE with sides 2.5cm, you calculated as if the cross-section had an area of 2.5cm^2, so you need to multiply by 2.5
I also need to remind you that in previous LCs, it has said, "Use 3.14 as pi," so the answer will be slightly lower

wikipedia defines cross-section like this "a cross-section is the intersection of a body in 3-dimensional space with a plane", it doesn't talk about a square, how could I know :/

Wow, wikipedia has the worst definition I've ever seen. "Cross-section" is the fancy word for "all the points intersected by a plane." For example, a cross section of a cylinder can be either a circle or a rectangle, depending on how you slice it.

When I think of the hoop, I think of it like a hula hoop. So you cut across the beam on 1 side. The cross section is the 2d shape you see when looking straight at the cut end. In this case, it's a square with sides of 2.5 cm. If the cut hoop was straight, it would resemble a prism.

btw for pi, I would refer you to LC #298, they use all the decimals in the solution.

that would make it 27865

English isn't my first language so I do not understand the square bit, does it mean it is a square with 2.5 sides or a square of 2.5 area?

Well it seems it is 2.5 sides, I tought it was 2.5 area too as english isn't my first language either.

The cross section is a square with sides that are 2.5 cm

Well I have a completely different answer to you Katana.

EDIT: Hmm actually, looking at it again it's a hoop not a soid cyclinder. Will that effect the answer because I have no idea how I'm going to find the volume of that hoop with so few given measurements :S

well both me and willzi came to about the same answers, (27865 with full pi, 27850 with 3.14) what did you obtain ?

I got less than 12000 for my answer.

I came up with something slightly different, but I have full work to back it up... anyone interested in getting another (manual) point of view?

if its somewhere around 11146 you forgot to multiply by 2.5, the cross section is a square of 2.5 cm sides, not 2.5 area.

just tell us your answer and how you got it, alsways interresting.

Hmm, well it might just be because it's midnight over here and I'm half asleep XD

I got a six figure answer starting with 5

well I just finished my working out and I came up with the same answer as you


not saying its right but seems we are using the same logic in our working out goodluck to all

Now I know I have to determine the hoop's inner and outer circumference... but the hard part is finding a radius...

Now here's how I'm approaching this one: I'm considering that the equation for a circle is x^2+y^2=r^2... in our situation, x, y, and r are all unknowns unfortunately...

I'm considering that I'm attempting to find the point of intersection with one of the edges of the bottom shelf.

I can figure out that x in our equation will be 69cm (because it's half of the shelf)...

This still leaves y unsolved... I can, however come up with an equation that involves r and y...

r-y=32 cm

Magic... I've found the Radius of the inner circle :p

69^2+(32-r)^2=r^2
4761+(1024-64r+r^2)=r^2
5785-64r+r^2=r^2
5785=64r
r=5785/64

Now the outer radius is easy to compute... simply add 2.5 cm

Now I'm treating this as a shell of a cylinder...

Volume for a cylinder is

(pi)(r^2)(h)

Volume for a shell is

(pi)((r1)^2)(h) - (pi)((r2)^2)(h)

So substituting:

(pi)(((5785/64)+2.5)^2)(2.5) - (pi)((5785/64)^2)(2.5)

Now to just do some simple computations... and multiply the answer by 7.85 g/cm^3... we get

28249.94359

And since we're rounding to the nearest gram, the answer will be

28250

Hmm, I think it must be the fact that's I'm doing a cylinder then. HOw are you workuing this out Fluffy?

Hmm, I got a different radius to you. 97.5 etc