## anonymous 5 years ago A partial sum of an arithmetic sequence is given. Find the sum. 4 + 9 + 14 + . . . + 484 need help

1. anonymous

The sum forumla you may find useful is $S_n = \frac{1}{2} \cdot n(a+l)$ You just need to find the number of terms...

2. anonymous

(Where a = first term, l = last term, n = number)

3. anonymous

I cant find n though

4. anonymous

Hint: The nth term = (n-1)d, so 484 = (n-1)*4 => n-1 = 484/4

5. anonymous

sorry, not 4 :/

6. anonymous

a+(n-1)d ***

7. anonymous

=>484 = 4 + (n-1)*5

8. anonymous

so n is 121. because 484/4= 121

9. anonymous

No sorry I misread it, see the post below.

10. anonymous

the post below??

11. anonymous

a+(n-1)d =>484 = 4 + (n-1)*5