SOLUTION: Find 1+2+3+4+...+140, the sum of the first 140 natural numbers

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Question 1109179: Find 1+2+3+4+...+140, the sum of the first 140 natural numbers
Found 2 solutions by ikleyn, Alan3354:
Answer by ikleyn(52788) About Me  (Show Source):
You can put this solution on YOUR website!
.
= %28140%2A141%29%2F2 = 70*141 = calculate it on your own . . .


See introductory lessons on arithmetic progressions
    - Arithmetic progressions
    - The proofs of the formulas for arithmetic progressions
    - Problems on arithmetic progressions
    - Word problems on arithmetic progressions
in this site.

Also,  you have this free of charge online textbook in ALGEBRA-II in this site
    - ALGEBRA-II - YOUR ONLINE TEXTBOOK.

The referred lessons are the part of this online textbook under the topic "Arithmetic progressions".


Save the link to this textbook together with its description

Free of charge online textbook in ALGEBRA-II
https://www.algebra.com/algebra/homework/complex/ALGEBRA-II-YOUR-ONLINE-TEXTBOOK.lesson

into your archive and use when it is needed.


Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
Find 1+2+3+4+...+140, the sum of the first 140 natural numbers
------------
1 to 140 is 140 numbers
1+140 = 141
2+139 = 141
etc
----
There are 70 pairs * 141
--> 141*70 = 9870