Q1) A Newspaper dealer sells 1 newspaper every 6 mins on average. You can assume it follows a Poisson Distribution.

a) Whats the probability that he sells exactly 3 newspaers in the next 6 mins? (My Answer: 0.83%)

b) whats the probability he sells at least 3 newspapers in the next 12 mins?

c) The dealer has 1 newspaper left to sell. Whats the smallest length of time he must wait to be at least 94% sure of selling it? (My answer: 16mins 52.8 seconds)

Q2) An electrical appliance lifetime follows a normal distribution with mean 530 hrs and SD 51 hrs. Calculate:

a) percentage of components that fail in under 600 hrs (My answer: 8.53%)
b) percentage that fail between 471 and 525 hrs (My answer: 33.72%)
c) lifetime that components can exceed with 95% confidence (My answer 613.64 hrs)

Q3) The journey to or from work has a mean of 67 minutes and a standard deviation of 15 minutes. You can assume a normal distribution of journey times.

a) What's the probability the workers total traveling time to and from work is more than 151 minutes? (My Answer: 28.43%)

Hi. Do you have a question? It would be a good idea to read this.

My question is:

Are my answers correct or incorrect? And if incorrect please can you explain. Thanks

Your first one isn't right. I'm not going to just check all of your answers for you though. If you explain what you did to get each answer I would gladly tell you if you took the correct approach or where you went wrong (and heck if you do that much I probably would check your answers because you're actually showing some effort). But as it is I'm not compelled to just check them. But like I said your first answer isn't correct.

How do I write mathematical symbols here? I am trying to write my working but its awkward.

Q1a) By using this formula: http://www.bionicturtle.com/images/u...7F1lambda1.png

where Landa = 1 and x=3

I substituted the values in and got the answer 0.83%

Q1b) P(x=>3)

= 1 - P(x < 2)
= 1 - [P(0) + P(1) + P(2)]
Substituted the values in the formula
= 1 - [0.1353+0.2707+0.2707]
= 0.3233 => 32.33%

I have written it in Paint

Originally Posted by zkm1223
How do I write mathematical symbols here? I am trying to write my working but its awkward.
This post should get you started with that.

Originally Posted by zkm1223
Q1a) By using this formula: http://www.bionicturtle.com/images/u...7F1lambda1.png

where Landa = 1 and x=3

I substituted the values in and got the answer 0.83%
Then you're doing the math wrong somehow. You should be getting something like .0613. If you can't get that part it's going to be tough to get any of the remaining questions. Try to figure out where you were going wrong.

Oh yeah, I have double checked it and I must have put something wrong in the calculator. I am getting 0.0613. Please can you check the rest of my answers.

He's kind of telling you to show your work and maybe even to explain your reasoning.

Sometimes just writing down what you're doing and why you're doing it makes it clear to you what is wrong.
Be wordy. Sleep on it if necessary. Don't panic; you'll get this, sooner or later.

This forum is helpful. I wouldn't have stayed here if it weren't.

I have shown my working in the attachments in posts 7, 8 and 9.

Q1 looks good. Haven't had time to check the others though.