Answers

2016-07-17T12:09:49+08:00
An = a1 + (n-1)d

15/4 = 3 + (4-1)d
15/4 = 3 + 3d
15/4 - 3 = 3d
3/4 = 3d
3/4 / 3 = 3d/3
1/4 = d

Therefore, the common difference is 1/4
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