I guess this must happen all the time and I just have not noticed, but I see in 这个坏了，你去买个新的吧, that we just use 个 ge (a measure word/individual) by itself without 一 yī or any other number. Is this common and are we always to understand one if no number is stated? If so, could the 一 be dropped from the sentence, “爸爸给我买了一本书”? Now I see that I have often used 个 alone in 这个.
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