数学JJ求助

xinhz001

    

187.
        数集S consists of factor of 16, 数集T
consists of factor of 8, x belongs to S, y belongs toT，问the least possible vaule of x-y

JJ主人认为是-15,
我认为是-7
因为S=1,2,4,8,16即,X的可能值=1,2,4,8,16;
T=1,2,4,8,也既是y的值,要想x-y最小,那么,x取最小值,y取最大值,应该是1-8=-7
请NN们指点迷津