Keepie, Bunny, Vicky, Tukai, and Subbu have their birthdays on consecutive days, all between Monday and Friday.
- Keepie’s birthday is as many days before Subbu’s as Bunny’s is after Tukai’s.
- Vicky is two days older than Tukai.
- Subbu’s birthday is on Thursday.
Can you figure out whose birthday is on which day?
Time to solve: 5 minutes.
A few words on reasoning puzzles
This little puzzle belongs to the class of reasoning puzzles. It has the telltale signature of a reasoning puzzle—the puzzle is described as a few Statements on a few Things followed by a Question. The statements tell pieces of a story about the Things and are conditions on the Things.
The puzzle question about the Things follow the condition statements. To answer the question, the condition statements are to be analyzed to piece together the hidden story on the Things.
It is not always easy to analyze the statements of a reasoning puzzle. Experience in solving reasoning puzzles helps as this class of puzzles needs a special set of techniques.
For example, the puzzle statements are NOT NECESSARILY to be analyzed from the first to the last, one after the other. Take it as a hint and analyze first the most important statement.
Solution to Whose birthday on which day logic puzzle
The THINGS in the reasoning puzzle are the five persons: Keepie, Bunny, Vicky, Tukai, and Subbu. The unknown story about them are their birthdays.
This is where your experience in solving reasoning puzzles comes into play.
Think visually. Imagine the five weekdays as five empty slots. Your job is to put the right name into a weekday slot, the name whose birthday is represented by the weekday.
The five birthdays of five persons are to be ASSIGNED to the five weekdays. It is a one-to-one assignment puzzle—one birthday for a unique weekday.
The best way to represent the state of the story discovered so far is to use a logic table with five column headings as the five weekdays—Monday, Tuesday, Wednesday, Thursday, Friday. Part of story discovered in the form of birthday details are written under the suitable weekday heading.
First thought is to form five rows for the five names. When all birthdays are discovered, each of the five columns and rows will have one entry of a person name at the cross-section of the corresponding column and row.
In this form, the logic status table is large. We will instead use only one row to record the names of five. This is the compact logic status table.
Now we are ready to analyze the three logic statements.
Whose birthday reasoning puzzle first technique—Direct assignment first
The technique follows simple common sense. First statement to analyze should be the one that tells a part of the story that can be recorded in the logic table with certainty.
To be specific, the first statement should be the one that specifies a birthday assigning a person name directly under a weekday.
Such a statement is the third one: Subbu’s birthday is on Thursday. It allows us to be certain of one of the five unknowns—we write Subbu under column Thursday. Following is the compact form of logic table.
Whose birthday reasoning puzzle second technique—Link reference technique
As soon as you get an entry in the logic table with certainty, you will try the second frequently used technique of link reference. This technique also follows common sense.
You will search for a statement that refers to the name Subbu and then analyze the statement searched out for more of certain assignments.
Such a statement is the first one: Keepie’s birthday is as many days before Subbu’s as Bunny’s is after Tukai’s.
Soon you realize the complexity of the statement—it does not give you a certain assignment directly and creates a number of possibilities that are confusing. Tukai’s birthday can even be before Keepie’s.
We keep the statement on hold and move on to analyze the second statement.
Whose birthday reasoning puzzle third technique—Temporary bonded structure
The most effective technique to be used when in confusion is to form a temporary bonded structure.
The second statement: Vicky is two days older than Tukai, does not specifically give us the birthdays of the two. Instead, it describes a positional relationship between the two. It says,
Vicky and Tukai are separated by two days with Vicky appearing before Tukai. This is the temporary bonded structure between the two.
When you try to place the two names separated by two days, you find that the two-name bond can be placed under the five weekday headings in only two valid ways one of which will finally be the only correct placement.
We can use effectively only the temporary bonded structure that has TWO possibilities. Fortunately, Vicky-Tukai bond also has only two possibilities.
The two possibilities of the bond are recorded below the logic table, as shown.
Whose birthday reasoning puzzle fourth technique—Eliminating one possibility by conflict
After creating a temporary bonded structure, our attempt will be to analyze the next statement to reduce the two possibilities to one certain assignment.
We’ll now analyze the first statement: Keepie’s birthday is as many days before Subbu’s as Bunny’s is after Tukai’s.
In the light of two possibilities of Vicky-Tukai bond, analyze the phrase—Bunny’s birthday is after birthday of Tukai.
The only possibility for placing Bunny after Tukai will then be in the slot of Friday.
It will be two days after Tukai’s birthday on Wednesday. Tukai’s birthday on Friday is impossible, as Bunny will then have no feasible birthday.
As Vicky is older than Tukai by two days, his birthday will be firmly placed on Monday and the remaining day Tuesday will be for Keepie. As Tuesday is two days before Thursday, the birthday of Subbu, the first part of the first statement, is also satisfied.
Final placement will then be:
Vicky-Monday, Keepie-Tuesday, Tukai-Wednesday, Subbu-Thursday and Bunny-Friday
Final solution shown.
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