Question 1136300
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The sum of all the terms of an arithmetic series is the number of terms, multiplied by the average of the first and last terms.  From the given information,<br>
{{{n((-12+22)/2) = 260}}}
{{{5n = 260}}}
{{{n = 52}}}<br>
There are 52 terms in the sequence.  The 52nd term is the first term plus the common difference 51 times:<br>
{{{22 = -12+51d}}}
{{{34 = 51d}}}
{{{d = 34/51 = 2/3}}}<br>
The common difference in the series is 2/3.