3, 7, 15, 39, 63, 127, 255, 511

The terms of the series are (2³ - 3), (3³ - 3), (4³ - 3), (5³ - 3), (6³ - 3), (7³ - 3),

(8³-3).

So, 27 is wrong and must be replaced (3³ - 3) i.e. 24.

The given sequence is a combination of two series :

I. 11, 20, 40, 74 and II. 5, 12, 26, 54

The correct pattern in I is + 9, + 18, + 36,.....

So, 40 is wrong and must be replaced by (20 + 18) i.e. 38.

The given sequence is a combination of three series:

I. 1st, 4th, 7th terms i.e. 2, 4, 9,.....

II. 2nd, 5th, 8th terms i.e. 3, 6, 12,.....

III. 3rd, 6th, 9th terms i.e. 4, 8, 16,.....

In each one of I, II and III, each term is twice the preceding term. So, 9 is wrong and must be replaced by (4 x 2) i.e. 8.

The correct pattern is x 2, x 4, x 2, x 4, .....

So, 550 is wrong and must be replaced by (320 x 2) i.e. 640.

The correct pattern is x 2 + 1, x 3 + 1, x 2 + 1, x 3 + 1,.....

So, 356 is wrong and must be replaced by (129 x 3 + 1) i.e. 388.

The correct pattern is - 192, - 96, - 48, - 24, - 12, - 6.

So, 48 is wrong and must be replaced by (92 - 48) i.e. 44.

The correct pattern is + 6, + 8, + 10, + 12, + 14.

So, 45 is wrong and must be replaced by (30 + 10) i.e. 40.

The correct pattern is x 3 - 4.

So, 654 is wrong and must be replaced by (218 x 3 - 4) i.e. 650.

Each term of the series is obtained by dividing the preceding term by 4.

So, 1536 is wrong and must be replaced by (1536 + 4) i.e. 384.

The correct pattern is + 4, x 2, + 4, x 2, .....

So, 132 is wrong and must be replaced by (68 x 2) i.e. 136.