In the decimal number series 24.3, 23.1, 20.7, 17.1, 12.4, which value is the odd one out if the intended differences should be simple multiples of 1.2?

Introduction / Context:
This question features a decreasing decimal series: 24.3, 23.1, 20.7, 17.1, 12.4. You are asked to find the odd one out. The differences between these decimals suggest a pattern based on a fixed step size, namely 1.2, and the term that breaks this regular difference pattern is the outlier.

Given Data / Assumptions:
The series is:

• 24.3
• 23.1
• 20.7
• 17.1
• 12.4

We assume that the intended structure is a sequence where each new term is formed by subtracting successive multiples of 1.2 from the previous term.

Concept / Approach:
We calculate the differences between consecutive terms and see whether they are multiples of 1.2. If the first three differences follow a clear pattern like −1.2, −2.4, −3.6 and the last step does not continue this rule, the final term is likely incorrect or out of place.

Step-by-Step Solution:
Step 1: Difference from 24.3 to 23.1: 23.1 − 24.3 = −1.2, which is −1.2.Step 2: Difference from 23.1 to 20.7: 20.7 − 23.1 = −2.4, which is −2 * 1.2.Step 3: Difference from 20.7 to 17.1: 17.1 − 20.7 = −3.6, which is −3 * 1.2.Step 4: The pattern so far is subtracting 1.2, then 2.4, then 3.6. These are −1.2, −2 * 1.2 and −3 * 1.2 respectively.Step 5: Following this pattern, the next difference should be −4 * 1.2 = −4.8.Step 6: Subtracting 4.8 from 17.1 gives 17.1 − 4.8 = 12.3.Step 7: However, the given last term is 12.4, not 12.3, so 12.4 breaks the intended pattern.

Verification / Alternative check:
We can reconstruct the correct sequence if we follow the rule exactly: start from 24.3, subtract 1.2 to get 23.1, subtract 2.4 to get 20.7, subtract 3.6 to get 17.1 and subtract 4.8 to get 12.3. This produces a very clean pattern where each step uses the next integer multiple of 1.2. Since 12.4 does not fit this pattern, it is natural to treat it as the odd one out.

Why Other Options Are Wrong:
Values 23.1, 20.7 and 17.1 all support the regular sequence of differences. Removing any of them would break the clear progression of subtracting 1.2, 2.4 and 3.6. 12.4 is the only value that fails to be exactly one of these expected steps away from the preceding term.

Common Pitfalls:
Since the discrepancy between 12.3 and 12.4 is very small, some students may overlook it and assume rounding. However, competitive exams often expect exact adherence to a numerical pattern. Paying close attention to decimal differences is important when working with series that use decimal step sizes.

Final Answer:
The term that does not fit the consistent difference pattern and is therefore the odd one out is 12.4.