Hi,

This is a thread to discuss some of your other favorite puzzles, riddles, brain teasers, armchair treasure hunts, etc.

To get started, here's an online puzzle hunt I've participated in before: Puzzlecrack. It's a week-long competition with clues given through the web page. Past competitions (and solutions) are still there for you to figure out.

Another similar one is Microsoft's College Puzzle Challenge.

Any other favorites?

-Klatuu

This is a thread to discuss some of your other favorite puzzles, riddles, brain teasers, armchair treasure hunts, etc.

To get started, here's an online puzzle hunt I've participated in before: Puzzlecrack. It's a week-long competition with clues given through the web page. Past competitions (and solutions) are still there for you to figure out.

Another similar one is Microsoft's College Puzzle Challenge.

Any other favorites?

-Klatuu

In that moment a math student will saw the problem, figure out, and jump out of the window.

EDIT: by the way, my whole reasoning was "they only give us one number, and it's for something that doesn't even have a name. The thing kinda look like a circle. I'm gonna say it's one so the answer is 20".

So out of curiosity, how do you actually know that AB? and AC? are the same length? Is it because of the right angles?

=> (AD^2) = (AB^2) + (BD^2)

=> AD = sqrt(AB^2 + BD^2)

By the way, there's a way to figure out AC and AB if you suppose those are equal. Of course, by knowing AD = 20.

When I said AB? and AC? I meant the ones that don't have names. Like, [AE] (the one with B on its way) and [AF] (the one with C on its way).

To know that [AD]=[AF], you need to know that [AE]=[AF], don't you?

My question was, how do you do that?

EDIT: Here, I changed the picture to show what I mean.

In my new picture, A isn't the center of the circle anymore.

In this case, it's obvious, since I wanted to show you what I meant. But how do you know that in the first picture, A is the center? What is the way to calculate it? Surely when you're just looking it's easy to get it wrong if it's just off the center, right?

In fact, you can say there's no actual answer (For lack of information), because we're just assuming it's a quarter of a Circle. If it were the quarter of a Elipse, for example, AE =/= AF and we're screwed, unless they also give us AE.

So, in typical Math fashion, I assume it's a Quarter of a Circle. If it's a quarter of a circle, by definition all the lines from the middle to the perimeter of the circle has the same lenght (Because that's the definition of the circle). (I think). Since AF is a line from the middle to the perimeter, and AD is also a line from the middle to the perimeter, then AF = AD.

You then solve it geometrical.