Which of the following numbers will replace the question mark (?) in the given series?
168,191,218,249,284,?

Let's find the difference between consecutive numbers in the series:
191−168=23

218−191=27

249−218=31

284−249=35

Now, let's look at the pattern among these first-level differences:

23
+4

​
27
+4

​
31
+4

​
35
The differences increase by +4 each time (double difference pattern). Following this rule, the next difference must be:

35+4=39
Therefore, the missing number in the series is:

284+39=323