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For which positive integer n do we have \( 1 + 2 + 3 + 4 + \ldots +  n = 10 \times n ? \)

 Jul 6, 2020
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The sum of the first n integers is given by n*(n+1)/2 

 

So you have   n*(n+1)/2 = 10*n

 

Solve for n.

 Jul 6, 2020

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