百分数 + of 后面的名词，如果是复数，可以不加定冠词。这是为了表达简练，相当于all aduilts in the US， all the adults in the US。例如：

1. 30 percent of reptiles, birds, and fish are currently threatened with extinction.  

目前，30%的爬行动物、鸟类和鱼类面临灭绝的危险。

来自柯林斯例句

2. In 1987, McDonald's captured 19 percent of all fast-food sales in the US.  

1987年，麦当劳占据了整个美国快餐业销售额的19%。

来自柯林斯例句

3. 85 percent of all American households owe money on mortgages.  

85%的美国家庭背有按揭债务。

来自柯林斯例句

4. Did you know? Forty percent of men have body image issues, compared with 60 percent of women.

40%的男性身体形象有问题。而60%的女性身体形象有问题。

《美容时尚英语》

5. But some statistics show that 68 percent of people are over the age of 65.

但是一些统计数据显示， 65 岁以上的人们中有百分之68。

《科普小杂文》

6.Eighty percent of pumpkins here are roasted.

这里有80%的南瓜都是烤的。