Multiple choice

What is the $21^{st}$ term of the arithmetic sequence $ -5, -2, 1, 4, 7 ......$

  1. $51$
  2. $55$
  3. $54$
  4. $53$
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B Correct answer
Explanation

This is an arithmetic sequence with first term a = -5 and common difference d = 3. The n-th term is a + (n-1)d. For n=21, term = -5 + (20 * 3) = -5 + 60 = 55.

AI explanation

The sequence is an arithmetic progression with the first term a = -5 and the common difference d = 3. Using the nth term formula, a_n = a + (n - 1)d, we substitute n = 21 to find the 21st term. This gives a_21 = -5 + (21 - 1)3 = -5 + 60 = 55.

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