SOLUTION: Find the sum of first 20 term of the series 1+1+2�2+1+2+3�3+1+2+3+4�4....

Question 1073261: Find the sum of first 20 term of the series 1+1+2�2+1+2+3�3+1+2+3+4�4....
Answer by Edwin McCravy(20056) (Show Source): You can put this solution on YOUR website!

1+1+2�2+1+2+3�3+1+2+3+4�4....

Separate it into groups to get the pattern

1 + 1+2�2 + 1+2+3�3 + 1+2+3+4�4....

Extend the pattern until there are 20 numbers
(we get the 20th number just as it bwgins the 
last group):

1 + 1+2�2 + 1+2+3�3 + 1+2+3+4�4 + 1+2+3+4+5�5 + 1

We do divisions first, and they're all 1's: 

1 +  1+1  +  1+2+1  +  1+2+3+1  +  1+2+3+4+1  + 1

1 +   2   +    4    +     7     +     11      + 1

Answer: 26 

Edwin

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