word problem

J

jshaziza

Junior Member
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Jan 26, 2007
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102
Use the formula S=n^2+n/2, where S is the sum of hte first n natural numbers. How many consecutive natural numbers beginning with 1 will give a sum of 120?

I really didn't understand this problem. All I know is that there are 15 consecutive natural numbers that will give a sum of 120. But I don't know how they want me to apply that to the formula. If anyone can explain it to me that would be great. Thanks.
 
\(\displaystyle \L\\\frac{n(n+1)}{2}\) is the formula for the sum of the first n numbers.

I suppose they want \(\displaystyle \L\\\frac{n(n+1)}{2}=120\).

Solve for n.
 
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