Question

Difficulty: Very hardNumber and Alphabet Series
Consider the following numerical series:
4,11,30,85,248,4, 11, 30, 85, 248, \dots
What is the numerical value of the next term in this series?

Answer: 735

Answer

735
Each term is generated by multiplying the preceding term by 3 and subtracting consecutive odd numbers starting from 1 (1,3,5,7,91, 3, 5, 7, 9). Therefore, the term following 248 is computed as (248×3)9=735(248 \times 3) - 9 = 735.

Step-by-Step Solution

1
Examine the multiplier and subtractor progression between consecutive terms.
Multiplier is constantly 3, while subtractors follow the odd number sequence 1,3,5,7,1, 3, 5, 7, \dots
Establishing a standard recurrence rule Tn=3Tn1(2n3)T_n = 3 \cdot T_{n-1} - (2n - 3) for n2n \ge 2.
2
Calculate the sixth term using the derived rule.
T6=(248×3)9=7449=735T_6 = (248 \times 3) - 9 = 744 - 9 = 735
The fifth term is 248, and the fifth odd integer to subtract is 9.

Key Concept

Mixed operation numerical series involving constant multiplication and arithmetic progression of subtractors
Estimated Time:2m 0s
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