NerdBird's Riddles - Tips'n'tricks

There are many ways to solve riddles like these, but if you want a clue, here's a well-known method that (usually) always work.

Example - general method - download table - back to the riddles

Example:

Consider the following simple problem about 4 girls each having a pet:

1. Alice owns the budgie
2. The dog is named Barkie
3. Sweetie is not the rabbit
4. Mr. Meouw belongs to Dorothy
5. Fluffy is not the budgie
6. The cat does not belong to Cathy
7. Beatrice is not the owner of Barkie
8. The cat is named Mr. Meouw.

Here are 4 "objects" with 3 "properties" (the girl's name, the kind of pet and the name of the pet).

First, sort the possible "properties":

Girl names: Alice, Beatrice, Cathy, Dorothy
Pets: Budgie, dog, cat, rabbit
Pet names: Barkie, Sweetie, Fluffy, Mr. Meouw

Now, insert these into a scheme like this:

Fill in the scheme with +'s for correct, - for wrong and leave the field blank if unknown.

Information 1 (Alice owns the budgie): Put a + in the (Alice, Budgie) field and – in (Alice, Dog), (Alice, Cat), (Alice, Rabbit), (Beatrice, Budgie), (Cathy, Budgie) and (Dorothy, Budgie). Information 2 (The dog is named Barkie): Put a + in the (Dog, Barkie) field and – in the other fields, analogously with information 1. Information 3 (Sweetie is not the rabbit) is easily included by putting a – in the (Rabbit, Sweetie) field. Information 4 (Mr. Meouw belongs to Dorothy) is added like information 1 and 2. This should make your table look like this:

Now, with this information, you can already conclude a lot. Follow the +'s:

We know that (Dorothy, Mr. Meouw) is a +, so what's true for Dorothy is true for Mr. Meouw and vice versa. Since (Dorothy, Budgie) is a -, then (Budgie, Mr. Meouw) is a minus too. And (Dog, Mr. Meouw) is false, so you can also put a – in (Dorothy, Dog).

The same goes for the (Alice, Budgie) field: This leaves a – in (Budgie, Mr. Meouw) (though it's already there) and in (Alice, Barkie). You should also include what you can find out from the (Dog, Barkie) information, but this is already there too. Now, your table should look like this:

Now, add information 5 (Fluffy is not the budgie) and 6 (The cat does not belong to Cathy):

Now, do this cross-checking again. And notice the Budgie-row: 3 negative fields, which means that the remaining must be positive: Sweetie is the name of the budgie. Your table should look like this:

Add more information, like 7 (Beatrice is not the owner of Barkie) and 8 (The cat is named Mr. Meouw.)

Watch the (girl name, pet name) part: The Barkie column tells us that Barkie must belong to Cathy, and that leaves (Beatrice, Fluffy) as the only possibility left. And in the (pet, pet name) leaves Fluffy as the name of the rabbit. This makes the table go:

Now we can use this to see that Barkie belongs to Cathy and Barkie is a dog, so we must put a + in the (Cathy, Dog) field. Similarly, we fill out the rest of the table like this:

This can be summarised in an "ordinary" table:

Finally, check with the original information that your conclusion is correct.

General method

Draw a table like the one seen above; if the property-names are A, B, C, D and E (such as name, age, flavour, style etc.), the table is made like this (each property split into the respective possible values):

Download a table in Word97

If you want a ready made table, you can download this Word97-document, which allows a maximum of 5 objects with 6 properties.