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

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(52797)   (Show Source): You can put this solution on YOUR website!
.

= = 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.

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    - ALGEBRA-II - YOUR ONLINE TEXTBOOK.

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

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Answer by Alan3354(69443)   (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
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