Select the number from among the given options that can replace the question mark (?) in the following series.
24.9, 23.6, 21, 17.1, ?, 5.4
- A10.5
- B11.9
- C9.6
- D12.1
Solution & Step-by-step Explanation
Let's compute the difference between successive terms in the series:
23.6−24.9=−1.3
21−23.6=−2.6
17.1−21=−3.9
Notice that the differences are multiples of 1.3:
−1.3×1=−1.3
−1.3×2=−2.6
−1.3×3=−3.9
Following the pattern, the next difference should be −1.3×4=−5.2.
Therefore, the missing term is:
17.1−5.2=11.9
Let's cross-check the last step with the next multiple −1.3×5=−6.5:
11.9−6.5=5.4
This perfectly matches the final term.
23.6−24.9=−1.3
21−23.6=−2.6
17.1−21=−3.9
Notice that the differences are multiples of 1.3:
−1.3×1=−1.3
−1.3×2=−2.6
−1.3×3=−3.9
Following the pattern, the next difference should be −1.3×4=−5.2.
Therefore, the missing term is:
17.1−5.2=11.9
Let's cross-check the last step with the next multiple −1.3×5=−6.5:
11.9−6.5=5.4
This perfectly matches the final term.