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What is the sum of the odd numbers from 1 to 73 (including 73)?

 

What is the sum of the odd numbers from 1 to 231?

 Jul 6, 2018
 #1
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N =(L - F) / D +1, where N=Number of terms, L=Last term, F=First term, D=Common difference.

N=(73 -1) / 2 + 1

N =37 terms

Sum = (F + L) / 2 x N

Sum = (1 + 73) / 2 x 37

Sum =1,369

 

Do exactly the same thing with numbers 1 to 231. If you don't make any mistakes, you should get:

Sum =13,456

 Jul 6, 2018
 #2
avatar+10372 
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So you can find the formula.

 

I checked the results with Excel.

 

laugh

 Jul 6, 2018
edited by Omi67  Jul 6, 2018
 #3
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Omi67:

The questioner wants the SUM of these ODD numbers:

{1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73} =37 terms. This is an "arithmetic sequence".

=1,369

 Jul 6, 2018
 #4
avatar+10372 
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At first I had misread the question.
I corrected the answer.

Sorry sad

 Jul 6, 2018
 #5
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Thanks, Omi67.

 Jul 6, 2018

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