ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Riddles For Adults

Updated on March 8, 2016

The 100 Coin Cluster

Here is my favorite riddle of all times. Think of the following scenario. You are blindfolded sitting at a table with 100 coins on it. You know that 10 of these show heads and 90 show tails. However, you don't know which of the coins show heads since you are blindfolded (and not a cheater). We will come to the task in a second but first lets talk about the options you have to complete this task.

You can create piles of coins by counting them with your hands. You are also allowed to flip as many coins and as often as you want. Now here is the tricky objective. You have to form two piles of coins which have the same number of coins showing heads in them. That does not necessarily mean that both piles have to be the same size. It also does not mean that both piles need to have 5 coins showing heads ( remember, you can flip coins and that affects the number of coins showing heads or trails). Both piles just need to have the same number of coins with heads up. Here is simple an example where one pile consists of 10 and the other pile of 90 coins. Since both piles comprise 3 coins showing heads, this would be a valid solution to the riddle.

Finding The Right Path

You are running down a path in a jungle trying to find your way out. Before your escape, a friend has warned you of a dangerous bridge that lies ahead of you. It might collapse when you try to cross. Unfortunately, he only remembered that this bridge came right after a fork but not on what side of the fork the dangerous bridge is. The other side of the fork leads you to a bridge that is safe to cross.

Your friend told you that at each side of the fork sits an oracle, and you can ask each oracle one question. He knows for sure that one oracle always speaks the truth, the other one always lies, and each oracle knows if the other oracle lies or not.

You arrive at the fork and spot the two oracles immediately. At each side of the fork you can see a bridge in the distance, and you have no idea which is the safe one. Assuming you hold your life dear, what question do you have to ask the oracles to be absolutely sure which is the safe route?

The Three Door Problem

You are in a game show where the moderator makes you one of three closed doors. You know that there is a price hidden behind one door and the other two are blanks. Of course, you don't know which door holds the price, so you pick the first door randomly. The moderator opens now one of the two doors you haven't picked and hides a blank.

Apparently, the price has to be either behind the door you initially selected or behind the other door. Now it is getting interesting. The moderator offers you the option to switch doors and go with the door you have ignored so far. The key question now is, do your chances of winning the price increase if you switch doors or not? To ask a bit more specific, does each door have a 50% probability to hold the price?

A little hint: Intuition might not be very helpful to solve this riddle

SOLUTION: The 100 Coin Cluster

I am sure you will find the solution ridiculously simple. You create two piles, one with 10 coins and the second pile with the remaining coins. You flip all 10 coins in the smaller pile and you have the same number of heads in both piles. That is all there is to it.

Lets look at an example. Assume 2 coins are in the small and 8 coins are in the large pile. After you flipped all coins in the smaller pile, you also have 8 coins showing heads. That is the same number as in the large pile. This works for any scenario you can think of ranging from zero to ten coins showing heads up after the flipping.

SOLUTION: Finding the Right Path

Actually one question will do the trick. You ask one of the oracles "what would the other oracle tell me, what the dangerous path is". The path the oracle tells you is actually the safe route out. Let us think about the two possible scenarios for a moment.

Maybe you address the honest oracle. Since it knows the other oracle would lie, it is going to tells us that very lie.

On the other hand, if you ask the liar what answer the honest oracle would give, it will falsify the honest answer of the other oracle. Instead of getting the dangerous path, you end up with the right path in both cases. Essentially by linking the behavior of both oracles, you are always lied to which allows you to determine the safe route.

SOLUTION: The Three Door Problem

Your chances of winning improve from 33% to 66% if you switch to the door you did not pick initially. Hard to believe? Lets play with three different scenarios and look at the outcomes if you switch doors. For simplicity, I am going to enumerate the doors with the letters A, B, and C and assume the price is hidden behind door A. The three rows show the outcome (last column "Final Door") if you pick initially door A, B and C, respectively.

Initial Door
Moderators Door
Final Door
Door A
Door B
Door C
Door B
Door C
Door A
Door C
Door B
Door A

Looking at the last column of the table above, we can see that in 2 of 3 cases, we ended up with Door A and won the price by switching doors. Apparently, switching doors improves our chances of winning to 66%


    0 of 8192 characters used
    Post Comment

    No comments yet.


    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at:

    Show Details
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the or domains, for performance and efficiency reasons. (Privacy Policy)
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)