Question

Refer to the following series and answer the question (all numbers are single digit numbers only). (Left) 4 2 1 5 7 9 8 7 3 4 3 5 6 2 1 5 1 5 2 8 5 6 9 7 4 7 3 (Right) How many such odd digits are there each of which is immediately preceded by an odd digit and also immediately followed by an even digit?

• A. 7
• B. 6
• C. 5
• D. 4

Answer 1

Answer:

C. 5

There are 5 such odd digits in the series.

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We need to look for a specific 3-digit pattern:
$\text{\textbf{Odd Digit}} \longrightarrow \text{\textbf{Odd Digit (Target)}} \longrightarrow \text{\textbf{Even Digit}}$

Let's scan the series from left to right to find all instances that meet this condition:

1. ... 1 5 7 9 8 ... $\rightarrow$ 7 9 8 (9 is an odd digit, preceded by odd 7, followed by even 8)

2. ... 9 8 7 3 4 ... $\rightarrow$ 7 3 4 (3 is an odd digit, preceded by odd 7, followed by even 4)

3. ... 3 5 6 ... $\rightarrow$ 3 5 6 (5 is an odd digit, preceded by odd 3, followed by even 6)

4. ... 5 1 5 2 ... $\rightarrow$ 1 5 2 (5 is an odd digit, preceded by odd 1, followed by even 2)

5. ... 5 6 9 7 4 ... $\rightarrow$ 9 7 4 (7 is an odd digit, preceded by odd 9, followed by even 4)

List of Matching Clusters:

• 7, 9, 8

• 7, 3, 4

• 3, 5, 6

• 1, 5, 2

• 9, 7, 4