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Tons of em! How about another abstract one? <img src="/ubbthreads/images/graemlins/cool.gif" alt="" /> <img src="/ubbthreads/images/graemlins/biggrin.gif" alt="" />

Here's some maths for a change: how to prove that 2 = 1. Not really a riddle, but a mathematical flaw. (Moeha! Especially for Raze: a real flaw! <img src="/ubbthreads/images/graemlins/badsmile2.gif" alt="" /> <img src="/ubbthreads/images/graemlins/silly.gif" alt="" /> )
It's a pretty well known one though, so you're likely to have seen it already.

Given: a = b

=> a˛ = ab
=> a˛ - b˛ = ab - b˛
=> (a + b)(a - b) = b (a - b)
=> (a + b) = b
=> a + a = a
=> 2a = a

=> 2 = 1 !!! <img src="/ubbthreads/images/graemlins/confused.gif" alt="" />

[color:"#324372"]Because a = b, (a - b) is 0 in the third line. To get from the third to the forth line, you divide both sides by (a - b). You divide by 0. That's the problem...[/color]

Another fairly simple one:

Travelling to town, you arrive at a cross-roads.

Northern sign reads: This way to the town.

Western sign reads: This way there be dragons. Two of these signs are false.

Eastern sign reads: This way there be dragons. One of these signs are false.

Which way to the town?