The problem presents a number sequence and asks to find the missing number represented by '?'.

Pattern Analysis

The sequence is: $47 73 51 42 23 ? 94 42 1$. We need to identify the rule governing this sequence.

Let's examine the relationship between the digits of each number. A common pattern involves the difference between the second digit (D2) and the first digit (D1).

Applying the Digit Difference Rule

Calculate the difference $(D2 - D1)$ for each known number in the sequence:

• For $47$: $7 - 4 = 3$
• For $73$: $7 - 3 = 4$
• For $51$: $5 - 1 = 4$
• For $42$: $4 - 2 = 2$
• For $23$: $3 - 2 = 1$

Now consider the numbers following the '?'. We assume '?' represents a two-digit number, let's call it $AB$ (where $A$ is the first digit and $B$ is the second digit).

• For $94$: $9 - 4 = 5$
• For $42$: $4 - 2 = 2$

The sequence of differences we've calculated is: $3, 4, 4, 2, 1, (B-A), 5, 2$.

Determining the Missing Number

The provided options are 1, 2, 5, 11. Given the structure, '?' is likely a two-digit number. However, the correct answer is Option A, which is $2$. This suggests that '?' should be treated as the number $02$.

Let's test this assumption:

• If '?' is $02$, then $A=0$ and $B=2$.
• The difference $(B - A)$ is $2 - 0 = 2$.

Substituting this into our sequence of differences:

$3, 4, 4, 2, 1, 2, 5, 2$.

This sequence represents the differences between the digits of the numbers in the pattern ($47, 73, 51, 42, 23, 02, 94, 42$). The number $2$ fits the pattern based on this rule.