Answer
The common ratio is -0.3. The fifth term is .00243. $a_{n} = 0.3(-0.3)^{n-1}$
Work Step by Step
We are given the terms 0.3, -0.09, 0.027, -0.0081. Since each term is multiplied by -.3 to get the next term the common ratio is -.3. The fifth term = the fourth term $\times$ -.3. (the common ratio). So the fifth term = -.0081 $\times $ -.3 = .00243. To write an equation for the nth term of the form $a_{n} = a(r)^{n-1}$ plug in the first term for a (.1) and the common ratio for r (-0.3) to get $a_{n} = 0.3(-0.3)^{n-1}$
