In the following series one number is wrong, Find out the wrong number.9, 12, 71, 158, 259, 368, 478.5

The pattern is as follows:

Taking difference

⇒ 12 – 9 = 3

⇒ 71 – 12 = 59

⇒ 158 – 71 = 87

⇒ 259 – 158 = 101

⇒ 368 – 259 = 109, (367 – 259 = 108)

⇒ 478.5 – 368 = 110.5 (478.5 – 367 = 111.5)

Taking difference again

⇒ 59 – 3 = 56

⇒ 87 – 59 = 28

⇒ 101 – 87 = 14

⇒ 109 – 101 = 8 (108 – 101 = 7)

⇒ 110.5 – 109 = 1.5 (111.5 – 108 = 3.5)

As we can observe the next number after the difference is half the previous.

But due to 368 the series is not following the pattern.

∴ 368 is wrong and should be replaced by 367.