Asem

So I was playing with a knife yesterday night and I cut my arm pretty deep. The knife went all the way to the bones but no arteries were damaged, the bleeding level wasn't that high. I immediately went to the hospital and the doctor stitched the wound up and gave me antibiotics. I felt a little bit dizzy when the nurse was cleaning the wound but thats understandable.

However, when I woke up now, I went to the bathroom and I felt extremely lightheaded and I almost fainted for some reason. Now why is that and how likely is it to happen again? is it just my brain comprehending the wound or is it something that I should worry about?

P.S. when I woke up I noticed that I was laying my head straight on the wound, and some blood escaped from it.

A train is due to arrive at Central Station at 09.30 daily. On ten successive days the number of minutes by which the train was late were as follows.

3 0 4 -2 -3 13 8 -2 6 3

Show that the mean time of arrival was 09.33 and calculate the standerd deviation. (End of question)

For the mean part, I divided the sum of these values by 9 (since the 0 dosent count). The answer was 3 min, so 09.30 + 00.03 = 09.33

However my answer to the standard deviation part was wrong, the right one is supposed to be 4.80 min.

Any ideas?

The random variable X can take negative values and positive values. X is distributed normally with mean 3 and variance 4. Find the probability that X has a negative value.

What I did:

If X-N(3,16) and P(X<0)

then

P(Z < 1/4(0-3))

which is

P(Z< -0.75)

so the answer should be 0.22663

but the book says: 0.0668

Any Ideas?

I solved it as the following:

0.3 + 0.4 + (0.3*0.4) =

0.7 + 0.12 =

0.82

However the book says the answer is 0.58, so I guess I should subtract (0.4*0.3) from 0.3 + 0.4 rather than adding them together, the thing is, I cant understand why?