Identifying the Pattern:

To find the missing number in the series, we need to identify the pattern or rule that governs the sequence of numbers. Let's analyze the given series:

4, 13, 9, 17, 19, 19, 39, 23, ?, 29

First Step: Grouping the Numbers

To make the pattern more apparent, let's group the numbers in pairs:

(4, 13), (9, 17), (19, 19), (39, 23), (?, 29)

Second Step: Analyzing the Groups

Now let's analyze each group individually:

1. (4, 13): The second number is obtained by adding 9 to the first number.
2. (9, 17): The second number is obtained by adding 8 to the first number.
3. (19, 19): Both numbers are the same.
4. (39, 23): The second number is obtained by subtracting 16 from the first number.

Identifying the Pattern:

From the analysis above, we can see that the pattern alternates between adding and subtracting a certain number to obtain the second number in each pair. The alternating number sequence is as follows:

9, 8, 0, -16

Applying the Pattern:

To find the missing number in the series, we need to continue applying the pattern. Let's calculate the next number in the sequence:

(23, ?)

The next number will be obtained by adding the next number in the pattern to the previous number in the series:

23 + (-16) = 7

So the missing number in the series is 7.

Final Answer:

The number that will replace the question mark (?) in the given series is 7.