Answer:
1023.75
Step-by-step explanation:
The sum of a geometric sequence is
sum = a( 1 - r^n) / (1-r)
where a is the first term r is the common ratio and r^n is the nth term
We need to find the common ratio
r = 256/512 = 1/2
sum = 512 ( 1 - 1/2^12) / ( 1-1/2)
=512( 1-.000244141) / (.5)
=512(.999755859) /.5
=1023.75
