Which of the following numbers will replace the question mark (?) in the given series?
9, 15, 27, 33, 45, ?

Correct option is C

The given series is: 9, 15, 27, 33, 45, ?
From 9 to 15: 15−9=6
From 15 to 27: 27−15=12
From 27 to 33: 33−27=6
From 33 to 45: 45−33=12
The series alternates between adding 6 and 12.
Following this pattern, the next number should be
45+6=51.
Thus, the number that replaces the question mark is 51.
Correct Ans.(c).