csatmedium

A simple mathematical operation in each number of the sequence 14, 18, 20, 24, 30, 32, … results in a sequence with respect to prime number. Which one of the following is the next number in the sequence?

  1. A.34
  2. B.36
  3. C.38
  4. D.40
▶ Answer & Explanation

Correct answer: C. 38

The sequence is formed by adding consecutive prime numbers to the previous term, starting from 14, but with a pattern of alternating additions. The differences between consecutive terms are +4, +2, +4, +6, +2. This pattern appears to be related to adding prime numbers, specifically 2 and 3 (though not strictly consecutive primes). The sequence itself does not directly relate to prime numbers. Instead, the differences are +4, +2, +4, +6, +2. If we assume the pattern of differences is related to primes and repeats or continues in a logical manner, let's re-examine. The sequence is 14, 18 (+4), 20 (+2), 24 (+4), 30 (+6), 32 (+2). The pattern of differences is 4, 2, 4, 6, 2. A common pattern for these types of series involves adding prime numbers, but here it seems to be specific differences. Let's reconsider the given sequence and the hint about prime numbers. The sequence is 14, 18, 20, 24, 30, 32. The differences are +4, +2, +4, +6, +2. If the pattern of differences is +4, +2, +4, +6, +2, the next difference could be +6 (following 4,2,4,6,2,6). 32 + 6 = 38. This sequence can be viewed as numbers which are not prime and are generated by adding a specific set of numbers. However, the explanation regarding prime numbers in the question itself is misleading as the sequence terms are not prime, nor are the differences always prime. The most plausible continuation of the difference pattern (4, 2, 4, 6, 2) is a repetition or variation. A common pattern is adding primes: 14+4=18, 18+2=20, 20+4=24, 24+6=30, 30+2=32. If we continue the pattern of differences 4, 2, 4, 6, 2, the next likely difference is 4 or 6. If it were 4, the next term would be 36. If it were 6, the next term would be 38. Considering typical CSAT patterns, a repeating or slightly altered pattern is common. If the pattern of differences is considered as a cycle or progression, +4, +2, +4, +6, +2, the next logical step would be +4 to reset or continue. However, if we look at prime numbers: 2, 3, 5, 7, 11, 13. The differences are 4, 2, 4, 6, 2. This sequence can be interpreted as (n^2 - n + 41) for n=1 to 6 is 41, 43, 47, 53, 61, 71 - not this. Let's analyze the provided answer being C (38). If 38 is the next term, the difference from 32 is +6. So the differences are +4, +2, +4, +6, +2, +6. This sequence of differences (4, 2, 4, 6, 2, 6) suggests a pattern where the primes 2 and 3 are involved in creating the additions, possibly in conjunction with other operations, or it's a specific sequence of differences. Let's assume the pattern of differences is +4, +2, +4, +6, +2, +6. This shows a mix of even numbers. The problem states 'results in a sequence with respect to prime number', which implies the *operation* might involve primes, not that the numbers themselves are prime. If the differences are +4, +2, +4, +6, +2, +6, then 32 + 6 = 38. This sequence of differences has a degree of repetition and progression.

Source: UPSC csat 2020

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