Select the option that can replace the question mark (?) in the following series. VO39, TM35, RK31, PI27, ?

Correct — C. Split each term into its three tracks before you look at the options.

Rule: first letter −2, second letter −2, number −4.

V, T, R, P → N
O, M, K, I → G
39, 35, 31, 27 → 23

Reassemble the tracks and the missing term is NG23 → option (c).

Why the others are wrong

• (a)
  OH24 — In OH24 both letters have moved back only one place, and the number by three. Every step in this series is −2 on each letter and −4 on the number, and no step changes size.
• (b)
  MG22 — MG22 has the right second letter but the wrong first. P to M is three places back, not two, and 27 − 22 = 5 rather than the required 4.
• (d)
  MH24 — In MH24 all three tracks are wrong: the first letter drops three places, the second only one, and the number three.

An alphanumeric series carries two or three parallel patterns inside one term. Separate them before you even look at the options — letters in one row, numbers in another.

Here every track is a constant backward step: both letters −2 and the number −4. Once the tracks are apart the arithmetic is trivial.

The usual failure is not arithmetic at all. It is reading each term as a single object and matching it against the options by eye.

Key facts

• First letters: V, T, R, P, N — each −2.
• Second letters: O, M, K, I, G — each −2.
• Numbers: 39, 35, 31, 27, 23 — each −4.

Common traps

• Slipping a letter while counting backwards — P to N is two steps, not one.
• Assuming the number step must match the letter step — here it is −4 against −2.
• Choosing an option because its letters look right without checking the number.

No directly related past PYQ was found.