What should come in place of question mark (?) in the following number series?
20 13 24 11 28 ?

Options

A. 9
B. 12
C. 8
D. 7

Answer

To find the missing number in the series 20, 13, 24, 11, 28, ?, we can analyze the pattern of the series step by step.

### Step 1: Identify the two alternating sequences
The series alternates between two sequences:
1. The first sequence consists of the numbers in the odd positions: 20, 24, 28
2. The second sequence consists of the numbers in the even positions: 13, 11, ?

### Step 2: Analyze the first sequence (increasing)
The first sequence is:
- 20 (1st term)
- 24 (3rd term)
- 28 (5th term)

To find the pattern:
- From 20 to 24, we add 4.
- From 24 to 28, we add 4.

So, the pattern for the first sequence is to add 4 each time.

### Step 3: Analyze the second sequence (decreasing)
The second sequence is:
- 13 (2nd term)
- 11 (4th term)
- ? (6th term)

To find the pattern:
- From 13 to 11, we subtract 2.

We can assume the same pattern continues, so we subtract 2 from 11 to find the next term.

### Step 4: Calculate the missing term
Now, we subtract 2 from 11:
11 - 2 = 9

Thus, the missing term in the series is 9.

### Final Answer
The number that should come in place of the question mark (?) is **9**.

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