Find the 8th term in series? 2, 2, 12, 12, 30, 30, - - - - -

2023

Find the 8th term in series? 2, 2, 12, 12, 30, 30, - - - - -

  1. A.

    56

  2. B.

    60

  3. C.

    77

  4. D.

    70

Attempted by 22 students.

Show answer & explanation

Correct answer: A

Key insight: the terms come in repeating pairs and are generated by a simple formula depending on whether the position is odd or even.

  • Observe the pairs: 2, 2 ; 12, 12 ; 30, 30. Each pair repeats the same value.

  • Pattern rule: for position n (starting at 1), if n is odd use n^2 + n; if n is even use n^2 - n.

  • Verify a few terms: 1st = 1^2 + 1 = 2; 2nd = 2^2 - 2 = 2; 3rd = 3^2 + 3 = 12; 4th = 4^2 - 4 = 12; 5th = 5^2 + 5 = 30; 6th = 6^2 - 6 = 30.

Compute the 7th and 8th terms:

  1. 7th term (n = 7, odd): 7^2 + 7 = 49 + 7 = 56.

  2. 8th term (n = 8, even): 8^2 - 8 = 64 - 8 = 56.

Answer: 56

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