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Puzzle 421

• Place letters into the grid such that every row, column, and 2x2 block has letters (in any order) that form a common word.
• Each letter is only used once, and no letter is repeated in the rows/cols/blocks.
• Letters allowed: C O L U M B U S.

[Ref: ZWPU] © Alan Stillson and Frank Longo.

Puzzle 422

The BrainBashers mechanical computer is a very sensitive device, it consists of interlocked toothed gear cogs.

The largest cog has 168 teeth and the others have 49, 32 and 15 respectively.

By accident, Daniel started to rotate the largest cog.

How many revolutions must he rotate the largest cog make before the computer is back in its starting position with all of the cogs where they started?

Puzzle 423

Starting with the 6 in the bottom left corner, what is the highest total you can make, if you only move up or right, using the mathematical signs on the way?

Puzzle 424

A woman had three old coins - a silver dollar, a quarter, and a dime. Each coin was a little battered and had a piece missing. She found that exactly the same fraction had broken away from each coin.

What fraction of each was missing if the value of the remaining bits of coins was now exactly one dollar in total?

For this puzzle it can be assumed that ½ of a coin is worth ½ of its value.

[Ref: ZQJS] Based on a puzzle by Henry Ernest Dudeney.