Select the set of letters that, when placed in the blanks of the given letter series in order, will complete the series.
c _ c c _ d c _ c d _ d c c _ c d _ d d
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → ddcdcd
Here the blocks grow by one letter of each kind: one c and one d, then two of each, then three, then four (\(2+4+6+8=20\) places).
Block cd: c _ needs d
Block ccdd: c c _ d needs d
Block cccddd: c _ c d _ d needs c, d
Block ccccdddd: c c _ c d _ d d needs c, d
The series is cd ccdd cccddd ccccdddd, and the blanks in order are ddcdcd.