原题是这样的
Which number can you take away half & leave nothing?
哪个数你可以拿走（减掉）一半,什么也不剩?
回答是
0.5 - 1/2 = 0
0.5就是前面所说的Number,-1/2就是take away half,减掉一半,0就是nothing
From what numbre can you take and leave nothing?
什么数减去一半什么也不剩(得0)?