Question:medium

What is the missing number in the following sequence?

\[ 2,\ 6,\ 12,\ 20,\ \_ \_ \_ \_,\ 42 \]

Show Hint

The sequence \(2,6,12,20,30,42\) follows the pattern \(n(n+1)\).
  • \(36\)
  • \(32\)
  • \(30\)
  • \(24\)
Show Solution

The Correct Option is C

Solution and Explanation

Step 1: Understanding the Concept:
We need to identify the underlying pattern in the given numerical sequence to determine the missing term.

Step 2: Key Formula or Approach:

There are two common ways to approach this: 1. Method of Differences: Calculate the differences between consecutive terms and see if a pattern emerges. 2. Formula Method: Try to find a formula for the n-th term of the sequence. The numbers are products of consecutive integers.

Step 3: Detailed Explanation:

Method 1: Analyzing the Differences
Let's find the difference between consecutive terms: - \(6 - 2 = 4\) - \(12 - 6 = 6\) - \(20 - 12 = 8\) The differences are 4, 6, 8. This is an arithmetic progression with a common difference of 2. The next difference in the sequence should be \(8 + 2 = 10\). So, the missing term is \(20 + 10 = 30\). Let's check if the next term fits the pattern. The next difference would be \(10 + 2 = 12\). \(30 + 12 = 42\), which is the last term given. The pattern is consistent. Method 2: Finding a General Formula
Let's examine the terms themselves: - \(2 = 1 \times 2\) - \(6 = 2 \times 3\) - \(12 = 3 \times 4\) - \(20 = 4 \times 5\) The pattern for the n-th term \(a_n\) is \(a_n = n \times (n+1)\). The missing term is the 5th term in the sequence (\(a_5\)). \[ a_5 = 5 \times (5+1) = 5 \times 6 = 30 \] The next term is \(a_6\): \[ a_6 = 6 \times (6+1) = 6 \times 7 = 42 \], which matches the sequence.

Step 4: Final Answer:

Both methods confirm that the missing number in the sequence is 30. This corresponds to option (C).
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