Multiple choice

Directions: In the following series, one of the given terms is wrong. Find that term and mark that as your answer. 323, 221, 143, 79, 35, 15

  1. 79

  2. 143

  3. 323

  4. 221

  5. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The sequence is 323, 221, 143, 79, 35, 15. Differences: 102, 78, 64, 44, 20. This doesn't look like a simple pattern. Let's check prime factors: 323=17*19, 221=13*17, 143=11*13, 91=7*11, 55=5*7, 35=5*7. The pattern is products of consecutive primes: 17*19, 13*17, 11*13, 7*11, 5*7, 3*5. The term 79 is wrong; it should be 7*11 = 77.

AI explanation

The pattern multiplies each number by an increasing integer and then subtracts a decreasing cube: 7 × 1 + 5 = 12, 12 × 2 + 16 = 40, 40 × 3 + 102 = 222, 222 × 4 + 854 = 1740 (not 1742), 1740 × 5 + 8690 = 17390, and 17390 × 6 + 104268 = 208608. The number 1742 is wrong.

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