Number + 组 + Noun
组 is a measure word meaning "group" or "set," used to count collections of items that belong together. It is placed between a number and the noun it classifies. Use it for groups of equations, data sets, or teams.
老师把学生分成了四组。
Lǎoshī bǎ xuéshēng fēn chéng le sì zǔ.
The teacher divided the students into four groups.
请看第二组方程式。
Qǐng kàn dì èr zǔ fāngchéngshì.
Please look at the second set of equations.
每组派一个人来回答问题。
Měi zǔ pài yī ge rén lái huídá wèntí.
Each group should send one person to answer the question.