In the series 3, 9, 15.. what will be the 21st term ?

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

1. 36, 34, 30, 28, 24, ... What number should come next?

Answer: Option A

Explanation:

Pattern in the series is, -2, -4, -2, -4. So next term will be -2
24 -2 = 22

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}

Answer: Option B

Explanation:

Pattern is , +5, +7, +9
Missing Number = 19+9 = 28

Answer: Option A

Explanation:

Pattern is +5, +7, +9, +11
So next number will be +13
=> 33+13 = 46

Answer: Option B

Explanation:

Pattern is +5, +10, + 15, +20

Next number in the series will be 56 + 25 = 81