Aptitude - Odd Man Out and Series

Numbers are alternatively multiplied by 2 and increased by 3.

So, the missing number = 61 x 2 = 122.

Each number is double the preceding one plus 1.

So, the next number is (255 x 2) + 1 = 511.

Numbers are 1³, 2³, 3³, 4³, 5³, 6³.

So, the missing number is 7³ = 343.

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.