Given the first term, a1=20
Common ratio, r=0.5*1/2=0.25
A geometric sequence is represented by the following expression:
[tex]\begin{gathered} a_n=ar^{n-1} \\ \end{gathered}[/tex]We want to find the 15th term:
[tex]\begin{gathered} a_{15}=20(0.25)^{15-1} \\ a_{15}=7.45\times10^{-8} \end{gathered}[/tex]