Answer:
1968
Step-by-step explanation:
The given sequence is a finite arithmetic sequence.
Step 1: Determine the number of terms in the sequence
For an arithmetic sequence, the nth term:
A(n)=a+(n-1)d
In the sequence:
Therefore, to find which term the number 15 is, we have:
15=108+(n-1)(-3)
15=108-3n+3
15=111-3n
3n=111-15
3n=96
Number of terms in the sequence, n=32
Step 2: Find the sum of the sequence
For an arithmetic sequence with a given first and last term:
[tex]Sum, S(n)=\frac{n}{2}(a+l)\\ =\frac{32}{2}(108+15)\\=16*123\\$Sum of the sequence, S(n)=1968[/tex]
