The nth term of an arithmetic sequence is a + (n − 1)d. First term 5 and common difference 3: the 10th term is 5 + 9×3 = 32. Sequences as a set are in arithmetic sequences.
Count the jumps, not the term number
Ten terms means nine jumps. Forgetting the minus one is the usual miss. Mean of a list is a different leftover, in mean is sum over count.
The short list is in ACT Math formulas.
The bottom line
aₙ = a + (n − 1)d. Subtract one from n before you multiply.
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