Question 1131527
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Being able to use the formal algebraic methods to solve problems like this is important; you might need them for more difficult problems.  But for a simple problem like this one, you can do the same calculations without the formal formulas.<br>
The 15th term is 14 terms after the 1st term (15-1 = 14).
The difference between the 15th term and the first term is 56 (53-(-3) = 56).
So the common difference is 56/14 = 4.