Explanation:

Alright, let’s dig into this series: 17, 20, 25, 32, 43, 55.

- Series jumps:

20–17 = 3

25–20 = 5

32–25 = 7

43–32 = 11

55–43 = 12

- Look at the differences: 3, 5, 7, 11, 12.

These are almost all primes, except that 12 at the end.

- If we keep to the prime pattern after 11, the next prime should be 13 (not 12).

- So, after 43, add 13: 43 + 13 = 56.

But the series has 55 instead of 56.

- So, the odd one out is 55.

Option breakdown:

- 25 – flows with primes, fits pattern

- 20 – also fits

- 43 – fits as well

- 55 – doesn’t fit; mismatch with the prime gaps

- 32 – fine, fits the increasing prime difference.

Option 4, 55 is correct.