SOLUTION: how you get the sum of all the whole natural numbers greater than 89 and less than 101

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Question 604611: how you get the sum of all the whole natural numbers greater than 89 and less than 101
Answer by Edwin McCravy(20060)   (Show Source): You can put this solution on YOUR website!
how you get the sum of all the whole natural numbers greater than 89 and less than 101.
One way is just to add up the 11 numbers:

90+91+92+93+94+95+96+97+98+99+100 = 1045

The other way is to use the sum formula for an arithmetic sequence:

Sn = (a1 + an) 

where n = 11, 

S11 = (a1 + a11)

then use

a1 = 90, and a11 = 100

S11 = (90 + 100)

S11 = (190)

S11 = (190) = 1045.

Edwin

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