Can I express the numbers at more than one decimal point using 成? I know that if you want to express &quot;X-tenth(s)&quot;, you can use 成. For example:

增产三成
上座率有九成。

However, these only express the figure at one decimal point. If you want to express any figure at two or more decimal points, can you still use 成? For example:

黄金周五成北京市民选择的是4至6天的行程。 # one-decimal point (0.5)
黄金周五十五成北京市民选择的是4至6天的行程。 # two-decimal points (0.55)

Or if you can't, how can you express the figure usually?
Well, you could say 五成五 for 0.55 or 55%. 99% could be 九成九. 

For example, 九成九的人会参加这会议, meaning 99% of people will attend the meeting. 

Usually, people won't put that accurate. They may just say 大约五成, meaning 50% or so. But 几成几 is a normal expression.