00:01
So we're told that renata's saving money in an arithmetic sequence.
00:04
So let's write out the sequence.
00:06
They said that she saved $700 the first year, $850 to second, and so forth for 20 years.
00:15
So if she's doing this for 20 years, keep in mind that there would be 20 terms in the sequence.
00:20
So n would be equal to 20.
00:23
We want to figure out how much she is going to save in all.
00:26
So that means we want to find the sum of these 20 terms.
00:30
So we're trying to find s sub 20.
00:33
So to do this, we're going to use the formula, s sub n is equal to n divided by two times the quantity of two times a sub 1 plus n minus 1 times d.
00:45
So remember, n is 20 because there's going to be 20 years, so s of 20 is equal to 20 divided by 2 times, 2 times, well, a sub 1 is the first term, which is 700, plus n, which is 20, so 20 minus 1, and then we figure out our common difference...
