00:01
We're being asked to find the sum of this particular series.
00:04
So let's list the information that we know.
00:07
Well, we know the first term is 4, so a sub 1 is equal to 4.
00:11
And we know the last term in the series is 100, so a sub n is equal to 100.
00:16
And we can find how we get from one term to the next.
00:19
We simply keep adding 0 .5.
00:22
Therefore, our common difference is 0 .5.
00:27
So what we need to do is find our end value.
00:30
To do this, we're going to use the formula to find the end.
00:32
Term in an arithmetic sequence, which remember is a sub m equals a sub 1 plus the quantity of n minus 1 times d.
00:41
So let's substitute in the values that we know.
00:44
So when we do this, we're going to get 100 is equal to 4 plus the quantity of m minus 1 times 0 .5...