full transcript
#### From the Ted Talk by Daniel Finkel: Can you solve the vampire hunter riddle?

## Unscramble the Blue Letters

Let’s draw the chembar on a coordinate grid, with the Southwest corner at the point (0,0). The light passes through grid points with coordinates that are either both even or both odd. This is true even after it bounces off one or more walls. Another way of thinking about it is this: since the light travels at a 45 degree angle, it always crosses the diagonal of a unit square. teivarnlg 1 meter horizontally changes the x coordinate from even to odd or vice vsera. Traveling 1 meter vtlilacrey changes the y ctoroinade from even to odd or vice versa. Traveling diagonally – as the light does here – does both at once, so the x and y coordinates of any points the light passes through must be both even, or both odd. This oaobetvrsin is more pofuewrl than it seems. In particular, it means that we have a way to identify the kinds of points the light won’t ever go through If one of the coordinates is even and the other is odd, the lgiht will miss them. That means it’ll miss the top two corners of the room, since those points have one even and one odd coordinate. The Southeast corner is the only oitpon for the diffuser.
## Open Cloze

Let’s draw the **_______** on a coordinate grid, with the Southwest corner at the point (0,0). The light passes through grid points with coordinates that are either both even or both odd. This is true even after it bounces off one or more walls. Another way of thinking about it is this: since the light travels at a 45 degree angle, it always crosses the diagonal of a unit square. **_________** 1 meter horizontally changes the x coordinate from even to odd or vice **_____**. Traveling 1 meter **__________** changes the y **__________** from even to odd or vice versa. Traveling diagonally – as the light does here – does both at once, so the x and y coordinates of any points the light passes through must be both even, or both odd. This **___________** is more **________** than it seems. In particular, it means that we have a way to identify the kinds of points the light won’t ever go through If one of the coordinates is even and the other is odd, the **_____** will miss them. That means it’ll miss the top two corners of the room, since those points have one even and one odd coordinate. The Southeast corner is the only **______** for the diffuser.
## Solution

- light
- powerful
- observation
- traveling
- versa
- chamber
- coordinate
- option
- vertically

## Original Text

Let’s draw the chamber on a coordinate grid, with the Southwest corner at the point (0,0). The light passes through grid points with coordinates that are either both even or both odd. This is true even after it bounces off one or more walls. Another way of thinking about it is this: since the light travels at a 45 degree angle, it always crosses the diagonal of a unit square. Traveling 1 meter horizontally changes the x coordinate from even to odd or vice versa. Traveling 1 meter vertically changes the y coordinate from even to odd or vice versa. Traveling diagonally – as the light does here – does both at once, so the x and y coordinates of any points the light passes through must be both even, or both odd. This observation is more powerful than it seems. In particular, it means that we have a way to identify the kinds of points the light won’t ever go through If one of the coordinates is even and the other is odd, the light will miss them. That means it’ll miss the top two corners of the room, since those points have one even and one odd coordinate. The Southeast corner is the only option for the diffuser.
## Frequently Occurring Word Combinations

### ngrams of length 2

collocation |
frequency |

great chamber |
2 |

southwest corner |
2 |

light passes |
2 |

vice versa |
2 |

versa traveling |
2 |

### ngrams of length 3

collocation |
frequency |

vice versa traveling |
2 |

## Important Words

- angle
- bounces
- chamber
- coordinate
- coordinates
- corner
- corners
- crosses
- degree
- diagonal
- diagonally
- diffuser
- draw
- grid
- horizontally
- identify
- kinds
- light
- means
- meter
- observation
- odd
- option
- passes
- point
- points
- powerful
- room
- southeast
- southwest
- square
- thinking
- top
- traveling
- travels
- true
- unit
- versa
- vertically
- vice
- walls