Question

一道数学题求详解！要有解题过程！

There are 30 students each of which has one pen, one pencil, and one eraser. Then 26 students lost their pens, 23 students lost their erasers, and 21 students lost their pencils. What is the minimal possible number of students who lost all three things?

Answer 1

可以将已知条件转化成，剩下多少东西，然后把剩下的东西分配学生的，第1种情况：每个人只有1种东西；第二种情况：有学生最多有2种东西；第三种情况：有学生有3种东西；问题“最少全部没有”，也就是说尽可能多的学生手里东西，即为第一种情况

追问

谢谢。答案是多少？

追答

10

Answer 2

has one pen ：30-26=4
has one eraser ：30-23=7
has one pencil ：30-21=9
lost one (maximum)：4+7+9=20
lost all (minimal)：30-20=10