Question

已知关于x的不等式3(x-1)-a<=2恰有三个正整数解1,2,3,试求a的取值范围

六年级下《周周练与月月测》p75题目

Answer 1

3(x-1)<=a+2
x-1<=(a+2)/3
x<=(a+2)/3-1
x<=(a-1)/3

有三个正整数解1,2,3
所以3<=(a-1)/3<4
同乘3
9<=a-1<12
加上1
10<=a<13