Which number should be replaced with x in following series :

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

Answer: Option C

Explanation:

Please check the given sequence is combination of two series.
Series 1: 19, 38, 114, ...
Series 2: 2,3,4

In series 1, Pattern followed is *2, *3, so next will be *4
Next term will be
114*4 = 456

Answer: Option A

Explanation:

We can judge that it is A.P.
With 6 as difference
nth term in A.P. = a+(n-1)d
a= 3, n = 21, d = 6
So, 21st term will be = 3+(20)6 = 123

Answer: Option D

Explanation:

Numerators of the fractions in the given sequence are getting increased by 2, i.e. 1+2,3+2,5+2, so next will be 7+2 = 9

Denominators of the fractions in the series is getting doubled, 2*2 = 4, 4*2 = 8, 8*2 = 16, no next will be 16*2 = 32

So resulting fraction will be
\begin{aligned}
\frac{9}{32}
\end{aligned}

Answer: Option C

Explanation:

Please note that above sequence is containing 3 series
Series 1 : 8, 7, 6, (..)
Series 2 : 9, 10, 11, 12
Series 3 : 8, 9, 10

In series 1 pattern is -1. So missing term will be 6-1 = 5

Answer: Option A

Explanation:

Please look carefully at the series, its pattern is,
-1, +2, -1, +2, -1, so next will be +2
23+2 = 25