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Bob & Brenda - Reno: This series has run its course. Thanks to all the people worldwide who have followed this series and completed the caches even though they may never visit Las Vegas. Unfortunately, it seems that it is very hard to keep cache containers in these two parks without them being muggled. We'll probably redo this entire series, but place the caches in locations where they're less likely to be stolen.


Solving Puzzles VIII - Logic

A cache by Bob & Brenda - Reno Send Message to Owner Message this owner
Hidden : 05/26/2013
3.5 out of 5
1.5 out of 5

Size: Size:   micro (micro)

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Geocache Description:

Cache is not located at the posted coordinates.

Congratulations to Doctor A for the FTF!

This is the eighth in a series of caches that we hope will help cachers learn some of the tricks to solving puzzle caches. Although experienced puzzle solvers can jump in at any point in the series, each successive lesson is meant to build on concepts that were demonstrated in the previous caches. The first cache in the series contains some background information on puzzle caches as well as a link to the tools we use when solving puzzle caches.

This series is not meant to be an "end all" on how to solve every puzzle cache that exists. It is only a starting point on what to look for when you see a puzzle cache. If you go through this series, you should be able to solve most puzzle caches that have a difficult of 3 stars or less. If we gave away all our secrets, then we wouldn't have anything to do but put out lamp post caches.

This series of caches contains the following caches

Cache Techniques
GC4AFC5 Hidden Information
GC4AJ0W Lists
GC4ANJW Codes & Ciphers (Basic)
GC4ANKB Codes & Ciphers (Advanced)
GC4AZHP Images & Steganography
GC4AZHW Wordplay
GC4B2YM Mathematics
GC4B2YP Logic
GC4B2ZK Final Exam


Alert: There are downloadable files in our toolbox and printable copies (PDF) of the puzzles for the caches in this series. These files are not required to solve the puzzles, although they may be useful to you for both this cache series and other puzzle caches you solve. As the cache owner, I represent that these files are safe to download although they have not been checked by Groundspeak or by the reviewer for possible malicious content. Download these files at your own risk.


Logic puzzles are a type of puzzle where the reader is given a list of premises and must figure out what information can be deduced from them. These are known as syllogisms. Technically, Sodoku (both word and number versions) are a type of logic problem, but we covered them in earlier lessons. Another type of logic puzzle is the nonogram, where the solver must use number clues to create a binary puzzle. There is at least one in Las Vegas (can't remember which one it was) and here is one in Washington if you want to try your hand at one.

Logic puzzle caches that we've seen usually have multiple choice questions at the end. Each possible answer has a number associated with it that plugs into the coordinates.

For example: N 36 ab.cde

A. Who married Betty?

  • Charlie (3)
  • Bill (1)
  • Archie (0)

Solving Logic Puzzles

  1. Read the introduction to the puzzle. This has the details of the puzzle and the requirements needed to solve it. It also usually has the first clue to the puzzle.
  2. Scan the puzzle and create a list of all the items and categories that you are solving for (here we'll use husband, wife, vehicle, and last name).
  3. Create your crosshatch grid or table you'll use to solve the puzzle. Both of these solving methods are discussed below.
  4. Read each of the clues. Look for obvious positives (Bill married Anne) or obvious negatives (Archie never met Betty until his wife introduced them). In your grid, place a "O" where your positive items intersect (Bill/Anne) and an "X" anywhere your negative items intersect (Archie/Betty). Since most logic puzzles have a one-to-one relationship among items, any time you place an "O" in the grid, you can place an "X" in all the other items in that corresponding row and column.
  5. Read through the clues a second time (don't forget the clue that's probably in the introduction). Look for inferences that can supply more information. A clue that reads "The man who married Anne drives a Dodge", implies that Bill drives a Dodge because Bill married Anne. Add this information to your grid.
  6. Examine your grid to see if there are any answers that have been solved by earlier eliminations. Remember to transfer any positive items to other portions of your grid. If you missed the clue discussed in number 4 as applying to Bill (but marked that Anne has a Dodge), you can see that anything that applies to Anne also applies to Bill (and vice versa).
  7. Continue reading through the clues, picking up additional tidbits of information each time.
  8. Be careful when looking a negatives. The clue "Anne's marriage wasn't the one that immediately preceded Mr. Archer" tells us that Anne (and Bill) aren't the Archers. It doesn't tell us whether they were married before or after the Archers. It just says that in whatever position the Archers got married, Anne and Bill weren't the ones immediately before them.
  9. After reading through all the clues and you're still stuck, try making an assumption. Use one that has been narrowed down to two possilbities. Continue trying to solve the puzzle with the assumption that your guess was true until you run into a contradiction. Since your original assumption was false, then the other possibility must be true.

Crosshatch Grid

A crosshatch grid is probably the most common method used when solving logic puzzles.

Each bit of information is placed in the puzzle broken up by its category.

Assume we are creating a crosshatch grid for our sample puzzle described above where we're looking for the husband, wife, their last name, and what type of vehicle they drive.

We would list the 3 husbands' names (one per line) down the left side of our sheet.

Then we would list the wives' names, vehicles, and last names across the tops of the columns. It doesn't matter which order you put them in.

Finally, complete the grid by entering the categories in reverse order in rows down the page.

You should have a grid that looks like the one to the right.

Crosshatch Grid

Here is a good YouTube video from on how to interpret clues and fill in your crosshatch grid. The sound could be better, but you will get the general idea.


Tables are best used when the crosshatch grid gets to big to use. The example above only had four categories. Think of the size it would be if a puzzle had 8 categories. Tables are also better to use when one of the categories is in a specific order--such as days of the week. Since each "event" only happens once per time period, you would write those time periods down the left side of the table. Then each of the column headers would be the names of the categories (first name, last name, amount, etc.). As you read through each clue, you would write down the matching items in the proper row.

Here is a sample puzzle using a table:

Last week, Roadrunner published five new caches each day (Monday through Friday). On each day a different cacher was the first to find on three of the caches. Surprisingly, none of the cachers picked up the same combination of caches. From the information provided, for each day, determine the cacher, the geocoin that was in the cache (one was a FTF Geocoin), and the three caches where they were FTF.

  1. Each of the five caches was found exactly three times. Traditional caches were found every other day.
  2. One cacher found a puzzle cache and a traditional, but not on Friday. One cacher picked up both a puzzle cache and a multicache.
  3. Clay4 picked up an Earthcache and a traditional. The person who got the Minelab Geocoin picked up both an Earthcache and a traditional.
  4. The one who found the USA Geocoin, found a multicache and a letterbox and was the FTF at some point after zzbob and at some point before Clay4.
  5. Fyrcanine found the Pirates Booty Geocoin at some point after Kris32, who did not find a traditional. Kris32 was the FTF the day after the one who found the Geico Geocoin, who was not Monday's FTF.
  6. The ones who found the Geico Geocoin and the Pirates Booty Geocoin both awarded favorites to their multicaches.
  7. Allyn56 awarded a favorite to the puzzle cache.
Since we know we're using days of the week, we start by listing those down the first column and put our other category names across the top.

Clue 1 says that each cache was found three times and that traditionals were found every other day so they could only be found on Monday, Wednesday, and Friday so we list them on those three days.

Kris32 didn't find a traditional (clue 5), so she could only be Tuesday or Thursday. She found it the day after the one who got the Geico coin (5) and the Geico coin finder wasn't Monday (5), so Kris can only be Thursday and Geico has to be Wednesday.

Since Fyrcanine found the Pirate coin after Kris32 (5), those two can only fit on Friday.

Since the ones who found the Pirate coin and the Geico coin found multicaches (6) those could only be on Wednesday and Friday.

Logic Table
Clay4 found a traditional (3), so he has to be Monday or Wednesday. Clue 4 says someone found their caches before Clay4, so Clay4 can only be Wednesday.

The one who found the USA coin was after zzbob and before Clay4 (4), so the USA coin had to be Tuesday and zzbob has to be Monday. That person also found a Multi and a letterbox, so we can add those to the Tuesday row.

Logic Table
The only person who isn't listed yet is Allyn56, so he has to be Tuesday.

Clue 7 says Allyn56 found a puzzle cache, so that fills out the Tuesday row.

The Minelab coin finder found a traditional (3) so that couldn't have been Kris32 (5), so it has to be zzbob. This leaves the FTF coin for Kris32.

Since both Clay4 and the one who found the Minelab coin found an Earthcache, we can add those to zzbob and Clay4.

Logic Table
Traditionals were found on Monday, Wednesday and Friday. The one who found a traditional and a puzzle cache did not find theirs on Friday (2) and we already see on the chart that Wednesday is filled, that means zzbob's last cache was a puzzle. Logic Table
Since each cache type was found 3 times and we've only placed one letterbox, the Thursday and Friday caches have to include a letterbox.

That only leave the two remaining caches on Thursday, so they have to be the two that have only been found twice, the puzzle and earthcache.

Logic Table

This Cache

So, now you know how to solve a puzzle cache, here's one for you to try:

At this year's GeoAwards, 20 caches from around the world were nominated for cache of the year. Five cachers won trophies and platinum memberships for finishing first through fifth in the competition. Given the clues, can you determine the order of finish, the cacher, the name of the cache and the country the cache was placed in?

  1. The Canadian placed one position ahead of SheriffJohn in the judging.
  2. The trophy-winning Glowing Embers wasn't placed in Germany or Switzerland.
  3. Ragweed's cache is neither Manhatten Skyline nor Mona Lisa.
  4. The trophy winners in this year's competition are a German and a Swiss, Trees and Stumps, CandyCane, and the 1st place winner.
  5. The cacher from the United Kingdom, who isn't TickTock, placed higher in the event than The Clock Tower, which didn't place 5th in the contest.
  6. The trophy-winning Mona Lisa was not placed in Germany.
  7. Nightwolf, who didn't take first, and the cacher from Switzerland are both Reviewers.
  8. The cache from the United States finished one place higher than Glowing Embers, which didn't finish second.

Once you have solved the logic puzzle, answer these questions to find the cache located at

N 36° 13.ABC W 115° 15.XYZ

A. Where was the Manhatten Skyline placed?
  • United Kingdom (3)
  • United States (6)
  • Canada (4)
  • Switzerland (2)
  • Germany (5)
X. The order of finish (not necessarily consecutively) was:
  • TickTock, The Clock Tower, United States (9)
  • Canada, Ragweed, Glowing Embers (0)
  • CandyCane, Glowing Embers, United States (2)
  • Trees and Stumps, United Kingdom, Nightwolf (1)
  • Mona Lisa, Switzerland, Ragweed (8)
B. Who placed The Clock Tower?
  • Nightwolf (4)
  • Ragweed (1)
  • SheriffJohn (3)
  • CandyCane (0)
  • TickTock (5)
Y. If Ragweed was from Switzerland instead, he would have placed which cache?
  • Manhatten Skyline (7)
  • The Clock Tower (9)
  • Trees and Stumps (0)
  • Mona Lisa (2)
  • Glowing Embers (5)
C. SheriffJohn placed which cache?
  • Manhatten Skyline (3)
  • The Clock Tower (4)
  • Mona Lisa (2)
  • Trees and Stumps (8)
  • Glowing Embers (6)
Z. Glowing Embers is what type of cache?
  • Puzzle (6)
  • Earthcache (7)
  • Traditional (5)
  • MultiCache (4)
  • Event (3)


Additional Hints (No hints available.)

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