Mean (expected value) of a discrete random variable | AP Statistics | Khan Academy

[@merrowwood]

Through a series of unfortunate events, I was forced to teach myself a unit in half the time, and could not figure out the material. This has saved my grade. Thank you!

[@AnnieMartin-sg4ix]

I literally have tears in my eyes due to how helpful this is for trying to work through my Stats homework.

[@bttrlamb]

This video is just awesome - I'm sure many people are here for the sheer fact that they either: A) don't understand their professor and need help B) Their professor teaches this material horribly, and need help or C) Desperately need to know how to do this for class. Thank you Khan academy for going out of your way to explain these concepts! I thought I'd fail my class, but watching your videos motivate me and help me realize I can learn it because of how well you explain all these concepts. Thanks again!

[@w0nnafight]

who asked

[@mercilessanim]

I did

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​@@w0nnafightI did

[@the_violin_vlogger]

I did

[@that_guy1633]

I did

[@seanakazini]

Thank you so much. I'm stressing out and can't understand the textbook. Makes tons of sense now. :p

[@sdlion7287]

it's amazing how many books there are that are regarded as "good" but are so unfriendly and not kind to a student

[@kv4648]

Yeah only looks good to someone who already knows the subject

[@sanwellbeatz1630]

Im in tears...so happy i finally got this..thank u

[@halohaloj4268]

Thanks. This is so much easier than trying to understand ALEKS

[@danielgehrke66]

Thank you, Sal, it is good to see the notice (subscribe!) when some information, such as this problem and solution, is made available. Having an opportunity to reset thought is delightful, since this information can often be forgotten or become lost when a person has few practical reasons for every day use.

[@narendraparmar1631]

Easy explanation, Thanks

[@soundwave7502]

This is nice! My class ran out of time to cover this but it's in this nights homework :')

[@justjeechess]

extremely helpful!

[@meep7895]

i never really thought about expectation as a mean and that makes so much sense now cuz a mean is usually just assuming that all values have an equal probability but in this case they could have different probabilities

[@TheMitsosS]

Oh man those videos are soooo good. AMAZING job!!

[@TasyaAdzkiya]

I think the reason why we're taking the mean of it is because it's an expected value. We make an expectation from the data that we have to see the average or the most "typical" number from our data. That is because we're not going to pick a number willy-nilly-ly (a weird word, indeed). How else would you find an expected value other than taking the average of the data that you have? I think the rest of the formula is just a convention. I might be wrong, though.

[@Darmsofficial]

4 and a half minutes explains everything thank you very much

[@amylmcmurray5511]

Thank you so much for your videos! I don't know what I would do without your help!

[@collinsmwambo8485]

Thank you sir... Quite understandable

[@RandyDaGamer]

Thank you so much! I love this Channel! I love Khan Academy 🍀

[@grampton]

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[@fv4202x]

explaining wwith crosshair. was he pointing gun at the board?

[@fraktasticful]

Can we make that P_90(x) instead

[@KataokaTV]

goddammit bro, this made me laugh audibly in the library

[@Marc3ll3]

Your comment still have people like me lmao 4 years later! Hahaha ...

[@malteeaser101]

But if the outcomes of a random variable are arbitrarily mapped to a number, so let's say '1' if heads, then if '1' is the expected value then '1' means heads? I honestly don't understand what it means to say that '1' is heads and the idea of finding the expected value to be 1, what if I assign heads as 0 and tails as 1, wouldn't things be different if I assign heads as 1 and tails as 2? You said that we can assign a random variable in this way, though. It seems as though shape of the graph can be randomly changed depending on which numbers I assign to which outcome, too. Also, If we get two heads in a row then are these considered to be two separate outcomes that we count twice and say that they compose the event of getting two heads in a row, or are they considered to be one outcome that happens twice? I don't see how the sum of two upward facing dice equaling 7 is a single outcome that can be enumerated. I thought that would be an event that consists of many outcomes, hence another rehashing of question above, do we count the sum of 7 on a pair dice as one outcome that can happen in many different ways, due to many different combinations of the dice, or do we consider the outcomes to be the different combinations of the dice that come up and that the sum of 7 on upward dice is an event that is a collection of the student outcomes that meet that criterion?

[@kayleighsinnott7188]

Thank you!

[@BathroomOperator762]

Thank you

[@theblock2083]

pls change the crosshair, no way thats good in competitive.

[@nanangarifin5359]

Thank u

[@nick3550t]

Mean is like average value. Average have to divide by times to get only one value Mean have to combine pieces to make one value x.p(x) is to determine the size of each piece That's what i think.

[@LondonB99]

Do you not have to divide ?

[@samantham.2636]

question: how did you choose those probabilities? p(x)

[@mikeehumangit878]

How do u solve the P(X)?

[@chimukaonsonmapiki]

Can you explain why we multiply? Isn't it that mean = n × p where : n = fixed number of trials p = probability of success I can't see n on the question you answered Can you clarify

[@nick3550t]

Imagine the case have 100% probability. Let value = 3. Then 3*1(1 =100%) =3. So we expect you to workout 3 times in a week. Expected value is like average value. But the case involve probability. That's why we need to multiply with p. The reason why we don't have to worry mean overcome limit and divide by times of probability like average is that mean is made of combination of all probability(100%,1). Average have to divide by times to get only one value. Mean have to combine pieces to make one value. N x P is to determine size of each piece That's what I think. I might get wrong.

[@ebhehdbbeebbwbbw6559]

what if it's y does something will change?

[@kitty-ann5224]

How did you calculate the probability for 0?

[@lone_wolf2453]

1/7 = 0.14285714285

[@hiddenblue1598]

Base on the frequency

[@adequatequality]

Why is there a large COD hit marker on my screen...Anyways good video

[@osazeeehigiator3769]

not related to this question but can the x column be a negative number for example -2

[@hiddenblue1598]

Nahhh. It can't be.

[@RajveerSahay-jg9rb]

Why do I feel like im playing a FPS shooter math game with that cursor.😂

[@Cloudpuff888]

I'm only 16!!!!😊😊😊

[@Cloudpuff888]

Like wow

[@hiddensoul4137]

E y ?

[@abdullahiibrahim8103]

I just wanna to understand the discrete variables X is 0 1 2 3 4 wht does mean it days of the week or outcomes for wht plz anyone can explain to me

[@kitty-ann5224]

It's the number of times he'll work out in a week. So will he work out 0 days, 1 day, 2 days, 3 days or four days in the week. That's my understanding

[@abdullahiibrahim8103]

Thnks alot dear i understand

[@samuraisam6781]

*desk greet

[@hafsaimtiaz5832]

By putting X we are getting 0.1 , 0.15 like how...where are you putting these `×` value

[@PrEsHpEeSh]

The function is not so important when compared to the answer in this video. Eg. it is randomized answers that we are giving our "expected" value to

[@antwanwimberly1729]

🇺🇸

[@nushaierhamza7969]

but why multiply?

[@ryzelz]

GOD made more easier, the module has only fraction example.

[@whitetiger3987]

vay bee

[@srjh1528]

*discrete

[@williamzhou2581]

first

[@mikeehumangit878]

How do u solve the P(X)?

[@momenabdelmotaal8731]

thank you

[@dina-vn1ol]

*discrete

[@mathildahinape4215]

Thank you