Mandarin · Chapter 24 · Lesson 2 · Grammar primer
Approximation and rounding
Grammar for HSK 4.
The short version
左右 (zuǒ yòu) trails the number, 大概 (dà gài) leads it
Each Mandarin approximator owns a fixed seat, and swapping them breaks the sentence. 左右 (zuǒ yòu) always follows the quantity it softens, 大概 (dà gài) always comes in front, and both can appear at once so long as each stays put. 左右三十个人 (zuǒ yòu sān shí gè rén) is simply wrong.
三十个人左右 sān shí gè rén zuǒ yòu
差不多 (chà bu duō) undershoots, 左右 (zuǒ yòu) straddles
三十左右 (sān shí zuǒ yòu) means roughly thirty and could well be thirty-two. 差不多三十 (chà bù duō sān shí) means you have not reached thirty yet: twenty-eight, twenty-nine. Reaching for 差不多 (chà bu duō) when you meant 'about, possibly a bit over' is not a style slip, it is a factual error.
差不多三十个 chà bu duō sān shí gè
That's the gist. The full article goes deeper - more examples, the edge cases, the why - and the practice below scores like a vocabulary session and earns the same XP.
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10-question session
One question at a time, mixed across the exercises in this lesson. Miss one and it comes back round before the end. There are 24 in all: practise more afterwards if you want them.
Lesson 2 of 9 in this chapter