急求三道数学题，谢谢！

florence17UID: 3046472

1.The water level in a tank is lowered by 6 inches, then raised by 8 inches, and then lowered by 4 inches. If the water level was x inches before the changes in level, whihc of the following represents the water level, in inches, after the changes?
key: x-3/2

why not x-2?

2.For the line with equation y=a*x+b, a*b不等于0, the x-intercept is twice the y-intercept.
The slope of the line    1/2

Key: uncertain


这个intercept 究竟指的是距离 都是正的， 还是数 可正可负？ 国内数学学的不是后者吗？

3. Which of the following sets of numbers has the greatest standard deviation?
A -2,0,2
B -20, 21, 21.5


key: A

答案错了？


求指点！ :handshake

popol1991UID: 3285073

第二题我怎么记得是相等……在哪做的来着……

florence17UID: 3046472

老陈的数学快速突破上的题，可是我记的截距有正有负啊，有的题是按正负解的，有的是按距离算的。马上去看看OG，看看可能找到。

florence17UID: 3046472

The term x-intercept refers to the x-coordinate of the point at which a graph in the xy-plane intersects the x-axis; it does not refer to the point itself. The term y-intercept is used analogously.

这是math convention 上的，按此理解应该指的是数，x的横坐标，y的纵坐标