Explanation:
[tex]a_{5}=15\\a_{5}=\frac{a_{4}}{2}\\15=\frac{a_{4}}{2}\\a_{4}=30\\[/tex]
Each one is actually 1/2 of the one before so,
a5 = 15
a4 = 30
a3 = 60
a2 = 120
a1 = 240
