Select the option that can replace the question mark (?) in the following series. FM61, EK58, DI55, CG52, ?

Correct — A.

Rule: first letter -1, second letter -2, number -3.

F, E, D, C then B
M, K, I, G then E (positions 13, 11, 9, 7, so 5)
61, 58, 55, 52 then 49

Putting the three strands back together gives BE49, option (a).

Why the others are wrong

• (b)
  CD44 — Its number is 44, eight below 52. The numbers fall by three each time, so the missing term has to end in 49.
• (c)
  BF48 — Its second letter is F, only one step back from G. The second letters fall by two — M, K, I, G — so E is required.
• (d)
  CE46 — Its first letter repeats the C of the previous term. The first letters fall by one each time, so B is what comes next.

A mixed letter-number series runs three independent strands side by side, and each has to be read on its own.

Separate them before doing anything else: the first letters, the second letters, the numbers.

Here the three steps are -1, -2 and -3. SSC likes that spread because a candidate who checks only the first letters still has two options alive, so the elimination has to run across more than one strand.

Converting the letters to positions makes the second strand obvious: M is 13, K is 11, I is 9, G is 7, so the next is 5, which is E.

Key facts

• F, E, D, C fall by one letter each time, so the next first letter is B.
• M, K, I, G are positions 13, 11, 9 and 7, falling by two, so the next second letter is E.
• 61, 58, 55, 52 fall by three, so the next number is 49.

Common traps

• Checking only the first letters, which leaves both BE49 and BF48 alive.
• Reading M to K as a single step because the two letters sit close together in the alphabet.

No directly related past PYQ was found.