Study this sequence of twenty-two elements: K 8 A # 3 R T % E 6 M @ 5 U B 9 D & I 2 P 7. If every vowel is struck out of it, which element then stands twelfth from the left end?

The vowels are A, E, U and I, standing fourth, ninth, fourteenth and nineteenth by count from the left. Striking them out leaves eighteen elements: K 8 # 3 R T % 6 M @ 5 B 9 D & 2 P 7. The twelfth of these is B. The twelfth element of the untouched sequence is @, which is what you get by forgetting to strike the vowels out; 5 and 9 stand eleventh and thirteenth in the shortened sequence, so either follows from a miscount of one.