How correct is to ignore using the verb if it is repeated. example:
A traditional teacher can teach hundreds, another one who uses technology thousands.
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Leaving a word (even a verb) out of a sentence instead of repeating it, when the reader or listener will be able to tell from hearing or reading the rest of the sentence what the missing word would be, is a perfectly "correct" way of using English. It even has a name: "ellipsis." (Also known as "gapping." But these two terms are not important to know if you just want to learn basic English!)
Scholars who study English usage have found that certain kinds of ellipsis of this sort are used more commonly in written English than in spoken English.
Ellipsis has been a favorite tool of some of the best poets and writers of English.
(Note: If you are just beginning to learn English, it is probably best to avoid leaving out verbs or other words until you have become more experienced using the language.)