the company had about 20 notbook computers but only one- third ________ used regularly.Now we have

题目

the company had about 20 notbook computers but only one- third ________ used regularly.Now we have
the company had about 20 notbook computers but only one- third __were______ used regularly.Now we have 60working all day long.为什么用复数?不是小于一吗

答案

one-third 后面省略了（of them）,指20台笔记本中的约1/3,算下来应该是6-7台,因此要用复数.
全句：公司以前有大约20台笔记本电脑,但只有1/3经常使用.现在我们有60台全天候使用.