Medium
Find the missing letters to complete the series: aa_ba_aa_ba_
Explanation
Explanation
The series repeats the 6-letter block 'aabbaa' twice. Filling the blanks in order gives: a,a,b,b,a,a,a,a,b,b,a,a - so the four missing letters, in order, are b, a, b, a, i.e. 'baba'.
PRO TIP
Re-check your working by substituting the answer back into the original question.