Expressing an approximate numbers in ascending order
To express an approximate number, such as 3-4 or 20-30, we should say these sequential numbers in a row in ascending order.
To express an approximate number up to 10, we should say two adjacent numerals in a row, going in ascending order.
Scheme
number
number+1
Examples
他后退了一两步
He took a step or two backwards
tā hòutuì le yì liăng bù
我每周见他三四次
I see him three or four times a week
wǒ mĕi zhōu jiàn tā sān sì cì
Pay attention
We can not use 9 and 10 for expressing an approximate number because these numbers are from different digits. Stating 九十 would be understood as the number 90.
To express an approximate number for two-digits numerals, we should first state the tens digit once and then state the ones digit sequentially.
For example:
23-24 — 二十三四 
Scheme
(number of tens)
十
number
number+1
Examples
十三四个人
13-14 people
shí sān sì ge rén
五十八九只猫
58-59 cats
wǔshí bā jiǔ zhǐ māo
Pay attention
We also cannot consecutively name 99 and 100 or 999 and 1000 as an approximate number, because they are all from different digits.
If the approximate numbers are round tens, round hundreds or any larger digits, we should name the first numbers of each numeral and then name the round tens once.
For example:
200-300 — we name the first numbers of each numeral and then name the round tens
二三百 or 两三百
or 两三百 Scheme
number
number+1
十/百/千
Examples
四五十页
40 to 50 pages
sìwǔ shí yè
七八千本书
7000 to 8000 books
qībā qiān běn shū