Question:medium

53, 50, 45, 38, 29, ____

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When numbers fall quickly but not linearly, try “subtract consecutive odds/evens” or “add consecutive squares/cubes” before more complex rules.
Updated On: Jul 15, 2026
  • 11
  • 17
  • 18
  • 21
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The Correct Option is C

Approach Solution - 1

Step 1: Understanding the Concept:
Rather than only looking at the gaps between terms, check if each term fits a simple formula based on its position in the sequence.

Step 2: Key Formula or Approach:
Test whether each term equals \(54 - n^2\), where \(n\) is the position of the term (1 for the first term, 2 for the second, and so on).

Step 3: Detailed Explanation:
For \(n=1\): \(54 - 1 = 53\), matches the first term.
For \(n=2\): \(54 - 4 = 50\), matches the second term.
For \(n=3\): \(54 - 9 = 45\), matches the third term.
For \(n=4\): \(54 - 16 = 38\), matches the fourth term.
For \(n=5\): \(54 - 25 = 29\), matches the fifth term.
Since the formula holds for every given term, the sixth term (\(n=6\)) should equal \(54 - 36 = 18\).

Step 4: Final Answer:
The missing number is 18.
\[ \boxed{18} \]
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Approach Solution -2

Step 1: Understanding the Concept:
The gaps between consecutive terms, 3, 5, 7, 9 (all subtracted), are consecutive odd numbers, and consecutive odd numbers follow the general formula \(2k+1\) for the \(k\)-th gap, starting at \(k=1\).

Step 2: Key Formula or Approach:
Write the gap between term \(k\) and term \(k+1\) as \(2k+1\), and use \(k=5\) to find the gap between the fifth and sixth terms directly, without listing every earlier gap first.

Step 3: Detailed Explanation:
Checking the formula against the known gaps: for \(k=1\), \(2(1)+1=3\), matching the drop from 53 to 50. For \(k=2\), \(2(2)+1=5\), matching the drop from 50 to 45. For \(k=3\), \(2(3)+1=7\), matching the drop from 45 to 38. For \(k=4\), \(2(4)+1=9\), matching the drop from 38 to 29.
For the gap between the fifth and sixth terms, \(k=5\): \(2(5)+1=11\).
So the sixth term is \(29 - 11 = 18\).

Step 4: Final Answer:
The missing number is 18.
\[ \boxed{18} \]
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