Home > Thoughts > How many things between X and Y?

How many things between X and Y?

I’ve noticed that there are 3 possible answers for the question “How many things between X and Y?”.

I’ll give 3 examples to explain what I mean:

1. How many hours do you take between 2 PM and 7 PM?

The answer is 5 hours which is 7-2.

2. How many numbers are there between 2 and 7?

The answer is 4 numbers (The numbers 3, 4, 5, 6) which is 7-2-1.

3. How many numbers would you speak out if you count from 2 to 7?

The answer is 6 numbers (The numbers 2, 3, 4, 5, 6, 7) which is 7-2+1.

So why is the answer different in each case?

In the first question, you are asked to count the number of hours between 2 and 7. Actually the hour meant in the question is a period. From 2 to 3 is a period of hour, from 3 to 4 is another period and so on. The answer then is Y-X that gives you the number of steps (periods) that you’ll take from X to Y.

In the second question, you are asked to count how many numbers there are between 2 and 7. This time you’re asked to count the numbers themselves that you would visit between 2 and 7 … not the steps you’ll take. If you’re taking 5 steps from point 2 to point 7, then there are 4 points between them (that’s excluding the first and last point). So the answer is Y-X-1.

In the third question, it’s asked to count numbers that you speak out when counting from 2 to 7. This is to say in other words, “How many numbers between 2 and 7, inclusive?”. Let’s conclude the answer in a new style … Do you mind that a one step forward needs 2 points and 2 steps forward need 3 points and so on…? This is true! … Well if you got how I explained the answer of question 1 then the answer to this question is Y-X+1 because the number of steps is Y-X between X and Y!


The answer for the question “How many things between X and Y?” is either Y-X, Y-X-1, or Y-X+1 and the answer depends on what things you are trying to count!

  1. July 31, 2009 at 12:36 AM

    Nice topic 🙂

  2. riddek
    July 31, 2009 at 6:58 PM

    Nice Post 🙂

  3. Al Hussainy Mohamed
    February 15, 2010 at 7:48 AM

    Just awesome .. I’ve never thought about it that way .
    Keep it up bro :).

  4. Ibraheem Elsourogi
    January 1, 2011 at 10:49 AM

    It is very nice topic.

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