数学一道。不太明白[求助]

回家过年

小明将原有的书每10本放一层书架，又得了10，按12本一层，问原有多少本书？
1） before the addition of the ten books, xiaoming had less than 96 books
2） before the addition of the ten books,xiaoming had at least 26 books
A  设原来X层，后Y层，有10X+10=12Y--> X=1.2Y-1
因X、Y整数，Y必是5的倍数，
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谢了谢了

猫猫头

10a+10=12b (1),10a<96==>a<=9 so a can be1,2, 3,4,5,6,7,8代入(1)式,只有5可能 所以选A

[此贴子已经被猫猫头于2002-12-11 22:21:23编辑过]