Question

Difficulty: MediumNumber and Alphabet Series

Analyze the pattern in the numerical sequence given below:

4,9,20,43,90,?4, \quad 9, \quad 20, \quad 43, \quad 90, \quad ?

What is the value of the missing term that completes the sequence?

Answer: 185

Answer

185
Each consecutive term is calculated by doubling the previous term and adding an increasing integer (+1,+2,+3,+4,+5+1, +2, +3, +4, +5). Following this rule, 90×2+5=18590 \times 2 + 5 = 185.

Step-by-Step Solution

1
Examine differences or operations between adjacent terms
94=59 - 4 = 5, 209=1120 - 9 = 11, 4320=2343 - 20 = 23, 9043=4790 - 43 = 47
Identify the primary numerical increment pattern
2
Analyze the rule for term progression
The operations follow Tn=Tn1×2+(n1)T_n = T_{n-1} \times 2 + (n-1) for n2n \ge 2
Confirm consistency across all given terms
3
Compute the sixth term (T6T_6)
T6=90×2+5=185T_6 = 90 \times 2 + 5 = 185
Apply the addition increment +5+5 following +4+4

Key Concept

Number and Alphabet Series
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