Why do not we draw a boundary surface diagam within which the probability of finding the electrons is 100%?

A box contains 12 balIs out of which x are black.If one ball is drawn at random from the box,what is the probability that it will be a black ball? If 6 more black balls are put the box,the probability of drawing a black ball is now double of what it was before. find x.

a lot consist of 100 ball pens of which 16 are defective and others are good Subhana will buy a pen if it is good but will not buy if it is defective the shopkeeper draw one pen at random and given to her what is the probability that she will not buy it.

a lot consist of 100 ball pens of which 16 are defective and others are good Subhana will buy a pen if it is good but will not buy if it is defective the shopkeeper draw one pen at random and given to her what is the probability that she will buy it

Why do we see water droplets collected on the outer surface of a glass container?