のうち(で)
Usage
Xのうち(で) is used to indicate the total entity (X) when presenting a part or portion of X. "In; of; among"
Examples
一週間のうち、３日はアルバイトに行きます。
Out of a week, I work part-time for 3 days.
日本語を取っている学生のうち、三十％ぐらいは工業の学生だそうです
I've heard that about 30% of the students taking Japanese classes are engineering students.