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Math Help - How quickly can you add numbers from zero to one hundred without using a calculator?

  1. #1
    Member looi76's Avatar
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    How quickly can you add numbers from zero to one hundred without using a calculator?

    Question:
    Suppose you have a list of numbers from zero to one hundred. How quickly can you add them all up without using a calculator?

    Is there a simple way or a trick to add them quickly?
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  2. #2
    Eater of Worlds
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    Yes, there is.

    \frac{n(n+1)}{2}

    Now, let n=100

    \frac{100(101)}{2}=5050
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  3. #3
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    Quote Originally Posted by looi76 View Post
    Suppose you have a list of numbers from zero to one hundred. How quickly can you add them all up without using a calculator?

    Is there a simple way or a trick to add them quickly?
    100 + 1 = ?
    99 + 2 = ?
    98 + 3 = ?
    ...
    51 + 50 = ?

    How many such pairs are there?

    So what is the sum?



    See also this thread
    Last edited by stapel; March 23rd 2009 at 05:21 AM. Reason: Adding link to similar thread.
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