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 sequenj s7f+ak p vv9.nh/m5 ycyah3;ces is arithmetic and only one of1o gkq 9 jubm* yqpj5/zaow55: them is geomet5/ak5y:u1 wj qzbp5mj9q g*ooric.
$\begin{aligned}
a_{n} & =\frac{1}{3}, \frac{1}{4}, \frac{1}{5}, \frac{1}{6}, \ldots & c_{n} & =3,1, \frac{1}{3}, \frac{1}{9}, \ldots \\
b_{n} & =2.5,5,7.5,10, \ldots & d_{n} & =1,3,6,10, \ldots
\end{aligned}$
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 sixth term. Give your answer as a fraction.
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