15, 31, 63, 127, 255, (....)
Answer: Option B
Explanation:
Each number is double the preceding one plus 1.
So, the next number is (255 x 2) + 1 = 511.
5, 10, 13, 26, 29, 58, 61, (....)
Answer: Option A
Numbers are alternatively multiplied by 2 and increased by 3.
So, the missing number = 61 x 2 = 122.
1, 8, 27, 64, 125, 216, (....)
Numbers are 13, 23, 33, 43, 53, 63.
So, the missing number is 73 = 343.
3, 7, 6, 5, 9, 3, 12, 1, 15, (....)
Answer: Option C
There are two series, beginning respectively with 3 and 7. In one 3 is added and in another 2 is subtracted.
The next number is 1 - 2 = -1.
