Which letter cluster will replace the question mark (?) in the following series?
HM, KE, ?, WU, FS
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → PY
Each position of the cluster is checked on its own, using places in the alphabet; the count continues from A after Z and from Z before A. Here the gaps themselves change by 2 each time.
First letters H (8), K (11), ?, W (23), F: the gaps are 3, 5, 7, 9, so the missing letter is \(11+5=16\), P; then \(16+7=23\) gives W, and 9 places ahead of W are X, Y, Z, A, B, C, D, E, F, which matches F
Second letters M (13), E (5), ?, U (21), S (19): the first gap is 8 places back and the last is 2 places back, so the gaps are 8, 6, 4, 2 places back
6 places back from E are D, C, B, A, Z, Y, so the missing letter is Y (25); then \(25-4=21\) gives U and \(21-2=19\) gives S, which match the last two terms
So the missing cluster is PY.