The simple answer: like the
to in an infinitive, and like auxiliary verbs, prepositions can be distributed over parallel nouns, or repeated. That is, the nouns in the prepositional phrase can be the parallel elements, or the prepositional phrases can be the parallel elements. The same is true of other parts of speech. Examples will make this clearer, and may allow you to spot a pattern. Parallel elements are in bold below.
INFINITIVES:
I like to dance and yodel.
I like to dance the ländler, a traditional folk dance of my Hessian forebears, and to yodel.See the difference? If the elements are several words apart, the correct answer will repeat the
to.
PREPOSITIONS
I had trouble with questions 16 and 22.
I had trouble with question 16 and question 22.
I had trouble with question 16, a complicated combined rate problem involving a head start, and with question 22, an overlapping-set problem. I ran out of time
after question 16, but
during question 22.
I stumbled over question 16, but raced through question 22.See the differences? If the elements are several words apart, the correct answer will repeat the preposition, and if different phrases demand different prepositions, then both (or all) will be used. In the last example, the predicates are parallel.
Same sort of thing works with other parts of speech.
Now, real Standard Written English is more complicated than the GMAT on this issue, and sentences can actually have different meanings depending on whether you repeat or distribute the
to (or the preposition, whatever). For instance,
I like to drink and to drive means something very different than does
I like to drink and drive. The GMAT seems deaf to such distinctions, though.