soddy1979

I like thinking about the normal distribution graph when I think of these questions:

Picture the graph - these percentages encompass

68%: +/- 1 SD
95%: +/- 2 SD
99%: +/- 3 SD

So this question basically says you can go 1 SD below the mean. Thus, the entire upper half of the distribution (50%) is okay, and ONE (1) SD below is fine (half of 68%).

If you segment 6 pieces of the normal distribution, the right-most 4 distributions ( from -1 to 3 SDs) are encompassed.

I don't know how helpful this may be for you, this is just how I think of how to do these types...