本题目来源于试卷: Sequences & Series，类别为 IB数学
[问答题]
Only one of the following four sequences is arithmetic and only one of them r cs6kgyjfri*r43s b /v9-dw ++ pfzs ml5ryc0ga+wkz.4,m / ris ger, k+/z4lfcwpa.zs y mg+r05mometric.
$\begin{aligned}
a_{n} & =1,5,10,15, \ldots & c_{n} & =1.5,3,4.5,6, \ldots \\
b_{n} & =\frac{1}{2}, \frac{2}{3}, \frac{3}{4}, \frac{4}{5}, \ldots & d_{n} & =2,1, \frac{1}{2}, \frac{1}{4}, \ldots
\end{aligned}$
1. State which sequence is arithmetic and find the common difference of the sequence.
2. State which sequence is geometric and find the common ratio of the sequence.
3. For the geometric sequence find the exact value of the eighth term. Give your answer as a fraction.
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