June/July 2019 June/July 2019 - Page 6

A WICKED WITCH:

A witch owns a field containing many gold mines. She hires one man at a time to mine this gold for her. She promises 10% of what a man mines in a day, and he gives her the rest. Because she is blind, she has three magic bags who can talk. They report how much gold they held each day, and this is how she finds out if men are cheating her. Upon getting the job, each man agrees that if he isn't honest, then he will be turned into stone. So around the witch's mines, many statues lay!

Now comes an honest man named Garry. He accepts the job gladly. The witch, who didn't trust him said, "If I wrongly accuse you of cheating me, then I'll be turned into stone."

That night, Garry, having honestly done his first day's job, overheard the bags talking to the witch. He then formulated a plan...

The next night, he submitted his gold, and kept 1.6 pounds of gold. Later, the witch talked with her bags. The first bag said it held 16 pounds that day. The second one said it held 5 pounds. The third one said it held 2 pounds. Beaming, the witch confronted Garry. "You scoundrel, you think you could fool me. Now you shall turn into stone!" the witch cried. One second later, the witch was hard as a rock, and very grey-looking. How did Garry brilliantly deceive the witch?

The two keys here are: You want the two slowest people to cross together to consolidate their slow crossing times. You want to make sure the faster people are set up in order to bring the flashlight back quickly after the slow people cross. So the order is: 1-minute and 2-minute cross (2 minute elapsed) 1-minute comes back (3 minutes elapsed) 5-minute and 10-minute cross (13 minutes elapsed) 2-minute comes back (15 minutes elapsed) 1-minute and 2-minute cross (17 minutes elapsed).

Correct Answer Submitted By:

Jeff Lloyd, PE, Golder Associates

Cranium Challenge

May Solution

Please send you answers to

Thomas Selling via e-mail: thomasselling@me.com

Correct responses will be recognized in the future issues of the New Hampshire Civil Engineer.

June/July Challenge

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