Normal Distribution : P(more than x) where x is less than the mean

[UnlimitedEconZone]

Live longer please

you are saving generations who are taking math

thank you so much!!

[ExamSolutions]

@UnlimitedEconZone I hope to

[KurtLennon12]

@Examsolutions here you have got the value Z>-1.111 but what if you had got the value less than 0.5, which does not have the value even on the positive side of the graph......say -0.444 for example....if there's a video for that kind of problems I'd like to see them too!! Plz reply fast I have my exams after one week!!

[ExamSolutions]

@KurtLennon12 I have ones like this. Just look under the normal distribution on my website in the index and go through the tutorials.

[couchxpotatoe]

Wouldn't you subtract from1? Or would that give you the probability of something else?

[ExamSolutions]

@couchxpotatoe Not at all. If you took the probability from 1 it would give you the probability of being less than 118.

[couchxpotatoe]

@ExamSolutions I figured. Don't know why I confused that. Anyway, I owe you a million thanks.. Your videos are the only reason why my statistics class midterm didn't read like an alien language today.

[ExamSolutions]

@couchxpotatoe Thanks. Good luck.

[couchxpotatoe]

@ExamSolutions I figured. Don't know why I confused that. Anyway, I owe you a million thanks.. Your videos are the only reason why my statistics class midterm didn't read like an alien language today.

[KR811]

I have question what exactly do I do when the question is worded like this?

The elapsed time that takes from the time you call to order a pizza until it is delivered at your home can be modeled as a NORMAL random variable with mean (μ) = 30 minutes and Standard Deviation (σ) = 9 minutes. Answer the following:

1) What is the probability that the pizza will arrive WITHIN 15 minutes after you ordered?

I don't understand the WITHIN part. Is that less than 15 minutes or after?



[ExamSolutions]

@KR811 Draw the normal curve with 30 at the centre. Mark on 15 to the left and shade the area to the left of 15. It is this area (probability) you need to calculate. P(X<15)

[MrToys99]

thank you!!! :D

[ExamSolutions]

@MrToys99 Pleasure

[ThePsycheoutFanClub]

Can you please do a video or two on Permutation and Combination chapter it's like HELL to me i get confused at every single question :S it would be a GREAT HELP! Thanks :D

[ExamSolutions]

@ThePsycheoutFanClub No problem - Can you make a donation to Action Aid and I will do it for you.

[ThePsycheoutFanClub]

@ExamSolutions Sure... *donates... i can has video now pliss? :)

[ThePsycheoutFanClub]

@ExamSolutions lol i was kidding :P ... but for real where can i sign up? I'd love to help, be there video or none. :P

[fablungo]

Just one comment, would it not have been simpler to use the following rule:

P(A) = 1 - P(Not A)

P(Z>-1.11) = 1 - P(Z<-1.11)

It should get the same result but it would have saved considering a reflection.

[ExamSolutions]

@fablungo Yes it will give the same result but most tables do not have negative values and this tutorial was designed for those that have tables of z which are positive.

[fablungo]

@ExamSolutions Well in that case that's totally valid. Haven't yet got onto doing this stuff in statistics; i just know we get taught P(A) = 1 - P(Not A)

[MissPheonix1]

hello, you seemed to have made a little mistake.. at the end, from the normal distribution table, it's not 0.8655.... it's 0.8665

this video is very helpful by the way :)

[ExamSolutions]

@MissPheonix1 Ooops! Thanks for letting me know. I have now added an annotation

[simiya85]

you are awesome, I was just about to hit my head into wall. i am trying since three days to clear my concepts but you took only few minutes to do that. Impressive. Love u for making it easier for me.

[ExamSolutions]

@simiya85 : No probs - so pleased to have cleared that up for you.

[serenecelene]

thank you sooo much!!!

[ExamSolutions]

@serenecelene Pleasure

[Mey0522]

Thank you! 

[lalaloser223]

thank you so much u helped alot!

keep making these videos you are an excellent teacher

[ExamSolutions]

@lalaloser223 Will do and thanks

[reno69er]

im following your steps but for the maths q im doin the mean is = 150000 with the standard dev = 20000 and i have to find the probability of it failin before 80000..so wehen i take the "small x" (80000) form the mean (150000) and devied it im left with 79992.5 ....how do i work it out from there? ne help would b gr8

[ExamSolutions]

Thanks

[4132286]

love your videos really helpful!

[searchandupload]

if an exam question such as P(z<1.17) came up, would it require a look up table or just a chart with a curve?

[ExamSolutions]

Lookup table

[Diana0155]

Thank you for posting this video. My teacher assigned homework on this concept without teaching us how to work out the problems. Your explanations are clear and concise :)

[ExamSolutions]

Thanks - Hope the homework goes well for you now.

[SuperXd9]

1.11 in the table is 0.3665!! cant you see that???

1.11=0.3665

[ExamSolutions]

It is not! it is as I said 0.8665

[Dainyshmuck]

@SuperXd9 No its not...have another look he was right, it's 0.8665, even though he actually wrote 0.8655 as his final answer :)

[dragon29717]

These few minutes explain this concept much better than my Chinese teacher did for 2 class periods. Thanks.

[ExamSolutions]

Thanks - glad I could throw some light on it for you.

[fateater77777]

apparently chinaman couldnt

[mrckb]

is there another way to work out the thye value or what ever on the table with out using the table?

[Cold12345]

yes, finally one that speaks english

[sikms]

wow i understand everything ...but you just made one minor error, its 0.8665 not 0.8655 but good job explaining!

[xfriendyx]

thank you soo much :)

i have my exam next wednesday and I really got confused on these type of questions, and thanks to you, you have saved my life :D

thanks again

[NoneNamed]

Thank you :)

[Pranikki1]

Excellent video, thank you so much.

[CarrritosMont]

is there any way to work with the z score without the table

[fateater77777]

a really complicated equation

[roso614]

he just made it sound more complicated

[guitrheroadam]

hey thanks very much

so i can do this part now but what happens when you get e.g.

P(X<a)= 0.3

this is usually where the main marks are in the questions...

[Trombonerist]

you just took 8.39 minutes to explain something my teacher spent about a year trying to

thank you

[mju6767]

thanks alot

[MuslimahSouljette]

Thanks that helps a lot, and allows u to understand fully what to do when negative valus occur.