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A drill to remember (Posted on 2021-03-01) Difficulty: 2 of 5
A ball 13” in diameter has a 5” hole drilled
through the center.
How deep is the hole?

Author: Henry Dudeney

No Solution Yet Submitted by Ady TZIDON    
Rating: 4.0000 (1 votes)

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Solution Really, dude(ney)? (spoiler) Comment 2 of 2 |
The hole is 12 inches, top to bottom.

Draw a line through the center of the hole, following the path of the drill.  Draw two lines from a point P on the lip of the hole, one a perpendicular to the drill path and intersecting at point D and one to the center of the ball (C).  CPD is a right triangle, with CP = 13/2 and DP = 5/2.  This is half of a 5-12-13 right triangle, so CD = 12/2.  Double this to get the height of the hole, top to bottom.

  Posted by Steve Herman on 2021-03-01 18:39:31
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