In the following number series, exactly one term is incorrect. Identify the…
2025
In the following number series, exactly one term is incorrect. Identify the incorrect term.
7, 4, 5, 9, 20, 51, 160.5
Answer: B. 51 — Concept: A sequence can use a changing operation at each transition. If a transition uses a number k as both the multiplier and the addend, then the next term…
- A.
7
- B.
51
- C.
4
- D.
160.5
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Correct answer: B
Concept: A sequence can use a changing operation at each transition. If a transition uses a number k as both the multiplier and the addend, then the next term equals current term × k + k. Here, k increases by 0.5 after every transition.
Application: Apply k = 0.5, 1, 1.5, 2, 2.5, and 3 in order.
For k = 0.5: 7 × 0.5 + 0.5 = 4.
For k = 1: 4 × 1 + 1 = 5.
For k = 1.5: 5 × 1.5 + 1.5 = 9.
For k = 2: 9 × 2 + 2 = 20.
For k = 2.5: 20 × 2.5 + 2.5 = 52.5, whereas the series lists 51.
For k = 3: 52.5 × 3 + 3 = 160.5.
Cross-check: Replacing 51 with 52.5 makes every transition follow the same rule and also reproduces the final term 160.5.
Therefore, 51 is the incorrect term.