Answer:
16100
Explanation:
n = 100
a1 = 15
a100 = 307
The first thing you have to do is solve for d
a100 = a1 + (n - 1)*d
307 = 15 + (100 - 1)*d
307 = 15 + 99*d
307 - 15 = 99*d
292 = 99 d
d = 292 / 99
d = 2.94949494
That's a real odd result, but it is what you get.
Sum = (a + L)*n/2
sum = (15 + 307)*n/2
Sum = 322 * 100 / 2
Sum = 16100 It looks like I didn't have to solve for d. The person who made this up sure didn't