In this number puzzle on digit patterns, select the four digit number that does not follow the same rule as the others: 7214, 3618, 3519 and 9436.

Introduction / Context:
Odd one out questions with four digit numbers often hide a pattern inside the digits rather than in the whole number. The pattern can involve sums, differences or products of certain digits. This question gives four numbers and expects you to identify which number follows a different rule. Detecting these internal digit relationships is a useful skill in quantitative aptitude and logical reasoning tests.

Given Data / Assumptions:

• The four digit numbers are 7214, 3618, 3519 and 9436.
• We are looking for a common digit based pattern followed by three numbers but not by one.
• Only basic operations on digits, such as addition, are expected.

Concept / Approach:
A common technique is to split each four digit number into two pairs of digits: the first two and the last two. Then we compare sums of these pairs. Often, three numbers will not satisfy a special relation and one number will. Sometimes the odd item is the one that satisfies the special property instead of the ones that do not. We must observe which interpretation creates a clear majority pattern.

Step-by-Step Solution:
Step 1: For 7214, add the first two digits: 7 + 2 = 9. Add the last two digits: 1 + 4 = 5. These sums are not equal. Step 2: For 3519, add the first two digits: 3 + 5 = 8. Add the last two digits: 1 + 9 = 10. These sums are not equal. Step 3: For 9436, add the first two digits: 9 + 4 = 13. Add the last two digits: 3 + 6 = 9. Again, the sums are not equal. Step 4: For 3618, add the first two digits: 3 + 6 = 9. Add the last two digits: 1 + 8 = 9. Here, the sums are equal. Step 5: Thus, 7214, 3519 and 9436 do not satisfy the property “sum of first two digits equals sum of last two digits”, while 3618 does satisfy it. Therefore, 3618 is the odd one out, since it behaves differently from the majority.

Verification / Alternative check:
We can quickly verify our conclusion by writing each number in the form AB CD and checking AB sum versus CD sum: 72 14 gives 9 and 5, 35 19 gives 8 and 10, 94 36 gives 13 and 9, and 36 18 gives 9 and 9. Only for 3618 are the two sums equal. Exam setters sometimes choose the unique item as the odd one out, even though it satisfies a more regular pattern. Here that is clearly the case.

Why Other Options Are Wrong:
7214 is wrong as the odd one out because its first pair and last pair of digits add to different totals, just like most of the other numbers. 3519 is wrong as the odd one out because it does not satisfy the equal sum condition and behaves similarly to 7214 and 9436. 9436 is wrong as the odd one out because, like 7214 and 3519, it also fails the equal sum test.

Common Pitfalls:
Many students initially test divisibility or prime properties of the whole numbers and see no clear pattern, which can be confusing. Others may try to overcomplicate the problem by using multiplication or difference operations on the digits. In these puzzles, the simplest operations such as adding digit pairs usually lead to the intended pattern. Remember that sometimes the number which follows a neat internal rule is the odd one out, which is the opposite of what students first expect.

Final Answer:
The only number for which the sum of the first two digits equals the sum of the last two digits, and hence the odd one out, is 3618.