The sum of the first n natural numbers is given by the formula S=1/2n(n+1). If the first of n natural numbers have a sum of 325, the value of n is

Question

This is one of my math homework questions and I'm very confused on it.

Answer 1

You’ve got a formula for the sum, and you’ve got the sum (325). Put them together:

(1/2)n(n+1) = 325

multiply by 2

n(n+1) = 2*325 = 650

n²+n-650 = 0

Solve this for n. This has two solutions, one of which is negative (useless for this problem) and one is positive (that’s the one to use).

 

if you’re still confused, ask some more.

Answer 2

325 = (0.5)n(n + 1)

650 = n(n + 1)

0 = n² + n - 650

0 = (n + 26)(n - 25

 

Can you solve for n and answer?