Question 943917
How many terms are in the sequence: 640,320,160,.......,5?
it is gp whose a=640   r=1/2=2^-1  n=? last terms is=5
last term =ar^n-1
5=640x(1/2)^n-1
5/640 =2^-n+1
1/128=2^-n+1
2^-7=2^-n+1
-7=-n+1
-7-1=-n
n=8