Question

Find the missing number in the series:
5 15 9 ? 11 33 13 39

• A. 9
• B. 18
• C. 27
• D. 36

Hint:

Each even-place term is 3 times the term before it.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The series looks like it is made of pairs of numbers. We must find the pattern in each pair and use it to get the missing number.

Step 2: Split into pairs:
Group the numbers as (5, 15), (9, ?), (11, 33), (13, 39).

Step 3: Find the rule:
In the pair (5, 15), 15 = 5 x 3. In the pair (11, 33), 33 = 11 x 3. In the pair (13, 39), 39 = 13 x 3. So the second number in each pair is 3 times the first.

Step 4: Apply the rule:
For the pair (9, ?), the missing number is 9 x 3 = 27.

Step 5: Check the options:
9 and 18 are not 3 times 9. 36 is 4 times 9. Only 27 fits.

Final Answer:
The missing number is 27. \[ \boxed{27} \]