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  1. Calculate the sum of the following arithmetic series:

    \(18 + 5 - 8 - 21 - ... - 164 \)


  2. Calculate the sum of the first \(25\) terms of the following arithmetic series:

    \[\frac{1}{4} + \frac{1}{2} + \frac{3}{4} + ...\]


  3. Find \(t_{15} \) and \(S_{15} \) of the following series:

    \(2.4 + 2.8 + 3.2 + ... \)