The following graphs have no scales assigned to them. Which ones could be density curves for a continuous random variable if they were provided with the right scale? Check all that apply.

http://i56.tinypic.com/wbw611.png

Question

The following graphs have no scales assigned to them. Which ones could be density curves for a continuous random variable if they were provided with the right scale? Check all that apply. 

http://i56.tinypic.com/wbw611.png

queelius · Answer

So, a PDF should be non-negative everywhere (it makes no sense to have negative probability). Also, if it is zero everwhere, no amount of scaling will fix it (0 * x = 0).

So, those two observations rule out which graphs?