Question 83780: How do I :
Find the sum of the first 400 natural numbers.
Found 2 solutions by jim_thompson5910, scott8148:
Answer by jim_thompson5910(35256)   (Show Source):
You can put this solution on YOUR website! Since the first 400 natural numbers is
1,2,3,4,5,6,7...399,400
The sequence is
 where n starts at 1 and increments by 1
So to find the sum of the arithmetic sequence from 1 to 400 we can use this formula:
 where S is the sum, n is the number of terms (in this case 400),  is the first term (in this case 1), and  is the last term (in this case 400)
 Plug in n=400,  and 
 Add
 Multiply
 Divide
So the sum of the first 400 natural numbers is 80,200
Answer by scott8148(6628)  (Show Source):
You can put this solution on YOUR website! 400+1=401 ... 399+2=401 ... 398+3=401 ... this pattern leads to the solution ... 401*200=80200
in general, ((first term)+(last term))*(half the number of terms)
in this case (400+1)*200=80200
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