The world's 200 hardest brain teasers Mind-boggling puzzles, problems, and curious questions to sharpen your brain

The World's Hardest Brain Teasers

Here is a collection of my most interesting and mind-improving brain teasers. Many of the answers should give you a strategy for thinking, which will carry over to many other problems and provide you with thinking and problem-solving methods. There is no time limit for these questions (with exceptions as noted). Be aware that there may be more than one way to arrive at an answer to a question. Just remember, a person who can solve problems efficiently either knows a particular strategy for the type of problem or extracts something from the problem that is curious to him or her and that leads to the next step toward a solution.

1. Two U.S. coins add up to 30 cents. If one of them is not a nickel, what are the two coins?

2. Make one word from all the following jumbled letters:
o r e n o d w

3. In miles per hour, what is the average rate of a car going 20 mph and traveling back the same distance at 60 mph?

(a) 30
(b) 40
(c) 50
(d) 60
(e) cannot be determined unless the distance is given

4. If you don't know the meaning of the word PRECURSORY, which of the following words do you think means the opposite of PRECURSORY?

(a) flamboyant
(b) succeeding
(c) cautious
(d) simple
(e) not planned

5. An explorer found a silver coin marked 7 BC. He was told it was a forgery. Why?

6. I have only nickels, dimes, and quarters and have at least one of each type of coin. The total number of coins I have is fifteen and the total value of all the coins is $1.00. How many of each coin do I have?

7. A malicious computer program informs a user that it has "kidnapped" an important file and that what happens to the file will be based on the next statement to be typed by the user. If the user types a false statement it will delete the file, and if the user types a true statement it will change the file's name so it can never be found. The user types a statement that makes the computer unable to perform or shut down. What could the user have typed?

8. Terry is half as old as Alice was when Alice was five years older than Terry is now. How old is Terry now?

9. IMAGINARY NUMBERS is to REAL NUMBERS as

(a) spiritual : global
(b) infinite : finite
(c) prime : rational
(d) negative : positive
(e) disordered : ordered

Excerpted from The World's 200 Hardest Brain Teasers by Gary R. Gruber All rights reserved by the original copyright owners. Excerpts are provided for display purposes only and may not be reproduced, reprinted or distributed without the written permission of the publisher.

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