Which number should be replaced with x in following series :

2, 3, 5, 7, 11, x, 17

Answer: Option D

Explanation:

Given sequence is combination of two series
Series 1 : 1,3,6,10,..
Series 2 : 1,9,36,100,225

In series 1 pattern is +2, +3, +4. So next term will be
10+5 = 15

Answer: Option A

Explanation:

Pattern in the series is *2+1, *2+2, *2+3,.....

Term which replaces the question mark in the series is
121 * 2 + 6 = 248

Answer: Option D

Explanation:

Pattern is, -1, -2, ..,.. , -5

So -3 and -4 will fill the blanks to make it a pattern.

Next number will be 17-3 = 14

Answer: Option C

Explanation:

Pattern for the given series is, +8, +8, +16, +16, +24

So next will be +24, 73+24 = 97

Answer: Option C

Explanation:

\begin{aligned}
\text{Pattern is }\\
+1^2-1, +2^2-1, +3^2-1,+4^2-1 \\
5^2-1 = 28 + 24 \\
= 52
\end{aligned}