15 and 5 are the first two terms in a geometric sequence. What is the arithmetic difference between the 7th term and the 9th term?  Pick.
A) (40/3) * (1/3)^7	B) (40/6) * (1/3)^7	C) (40/9) * (1/3)^7	D) (1/3)^7	E) (100/3) * (1/3)^7
Common ratio = 5/15 =1/3   7th term = 15*(1/3)^7   9th term = 15*(1/3)^9   Difference = 15 * ((1/3)^7 - (1/3)^9)   = 15 * (1/3)^7 *(1 - (1/3)^2)   = 15 * (1/3)^7 * (8/9)   = (120/9) * (1/3)^7....   = (40/3) * (1/3)^7   (40/3) * (1/3)^7
<result>A</result>
15 and 5 are the first two terms in a geometric sequence. What is the arithmetic difference between the 7th term and the 9th term?