Find the probability of pulling
a yellow marble from a bag with 3 yellow, 2 red,
2 green, and 1 blue– I’m assuming– marbles. So they say the
probability– I’ll just say p for probability. The probability of
picking a yellow marble. And so this is sometimes
the event in question, right over here, is
picking the yellow marble. I’ll even write down
the word “picking.” And when you say
probability, it’s really just a way of
measuring the likelihood that something is
going to happen. And the way we’re going to
think about it is how many of the outcomes from this trial,
from this picking a marble out of a bag, how many
meet our constraints, satisfy this event? And how many possible
outcomes are there? So let me write the possible
outcomes right over here, so possible outcomes. And you’ll see it’s actually
a very straightforward idea. But I’ll just make sure that
we understand all the words that people might
say, so the set of all the possible outcomes. Well, there’s three
yellow marbles. So I could pick that yellow
marble, that yellow marble, or that yellow marble,
that yellow marble. These are clearly all yellow. There’s two red
marbles in the bag. So I could pick that red
marble or that red marble. There’s two green
marbles in the bag. So I could pick that green
marble or that green marble. And then there’s one
blue marble in the bag. There’s one blue marble. So this is all the
possible outcomes. And sometimes this is referred
to as the sample space, the set of all the
possible outcomes. Fancy word for
just a simple idea, that the sample space, when I
pick something out of the bag, and that picking out of
the bag is called a trial, there’s 8 possible
things I can do. So when I think
about the probability of picking a yellow marble,
I want to think about, well, what are all of
the possibilities? Well, there’s 8 possibilities,
8 possibilities for my trial. So the number of outcomes,
number of possible outcomes, you could view it as the size
of the sample space, number of possible outcomes, And
it’s as simple as saying, look, I have 8 marbles. And then you say,
well, how many of those marbles meet my constraint,
that satisfy this event here? Well, there’s 3 marbles
that satisfy my event. There’s 3 outcomes that will
allow this event to occur, I guess is one way to say it. So there’s 3 right over
here, so number that satisfy the event or the
constraint right over here. So it’s very simple ideas. Many times the
words make them more complicated than they need to. If I say, what’s the probability
of picking a yellow marble? Well, how many different
types of marbles can I pick? Well, there’s 8 different
marbles I could pick. And then how many
of them are yellow? Well, there’s 3 of them
that are actually yellow.

## 51 thoughts on “Finding probability example | Probability and Statistics | Khan Academy”

1. JaneFord says:

What if you have a time series and want to compare to see the probability of another time series based on the first time series? Hope you understand my question.

2. ionuorah says:

Can someone tell me how one goes about ordering Khan's DVDs?

3. The Nick says:

I think somebody lost their marbles…

4. dailydoseofretard says:

400k views with 4 comments. now 5 because of me

5. Josh Rulz Gaming says:

6. Sugar Plum says:

Thank you! I was making it so much more complicated than it actually was 🙂

7. Pro Tanker says:

Thanks for the video.
Allah may bless you 🙂

8. Seldin Gardane says:

Here's a question that's been bugging me.

You have a sac of four marbles. A red marble, a yellow marble, a blue marble, and a white marble. If you pull two marbles out at a time, how many ways could you end up with a red marble?

Is it 6 ways or 3 ways?

RW, RY, RB
WR, YR, BR

To me, a pairing of Red / White is the same as White / Red and doesn't count as a different way. That being the case, the first three pairings are the same as the second three pairings and thus its only three ways instead of six. Since I don't know the answer I am left to only speculate as to whether my logic is accurate or flawed.

9. Nashie says:

Hi, I would like to know what are you using to write down the marbles etc…? Thank you ^^

10. Appreciate It says:

Thanks for making it more complicated I really needed that 🙄🙄😒

11. Falfieri says:

Why did i take prob and stat, what was i thinking

12. TeddyBearGaming101 says:

khan needs better wrighting

13. Kobe Rucker says:

IT WORKS IT WORKS…………THE DISLIKE BUTTON WORKS!!!!!😱😱😱😱😱😱😱😱😱😱

14. Polar bear polar bear says:

thanks

15. 10,000 subs with no video challenge says:

820,208 views but 394 likes and only 28 comments now. Wow…..

16. 10,000 subs with no video challenge says:

i think he's re watching the video or paying people.

did not understand any thing ….. the most stupid vedio

18. ocean 7777 says:

Thanks that's an amazing video

19. Breanna Leal says:

i hate math

20. Rahina Lakibul says:

iM SO CONFUSE

21. Brock Taulman says:

Fake

22. Joginder Pal says:

thanks it helped me alot

23. Sif the great grey wolf says:

I sure love meth!

24. magnus edosomwan says:

Understanding but confusing5

25. Aidan Braat says:

Anyone know what to do if it asks “What’s the probability of pulling a yellow marble twice?”

26. Patrick Tumulty says:

Sample Space is a very fancy word

27. Nic_INFINITE says:

maths is so easy

28. Monica Iqbal says:

thank you! i'm relearning statistics and this video was very helpful 🙂

29. Meystrio is thunder says:

I love math thanks sir

31. Daniel Reyes says:

help!!!

32. frozenfire says:

I've Always been hating Math. AND…still I DOwho said math is life?

33. Kaung Naung says:

Love u man you are awesome I am going to get a high score on this test now!

34. Ayesha Ayesha says:

I can not understand only please explain nicely ok

THANK YOU SIR

36. QüEëNïE Tīffy says:

Dear maths…you have officially made me lose my MARBLESSSS!!!

37. the alien's sister says:

38. abbeymore1 says:

Who can help me with a Business Statistics question?

39. Carl Johnson says:

Thanks

40. percy roland says:

Thanks for making it easy to understand

41. Kenen Chang says:

omg this man is a legend

42. Moto Moto says:

My teacher makes it seem harder than it really is

43. 계정이현제 says:

Thanks

44. Sheree Baptiste says:

Me:Watches video
Me:Does not understand

45. Zay Zay says:

1 Million views… WOW

46. suga glider ;-; says:

I still dont get it… i loterally have to work out whats the probability of rolling a 6 on a dice three times in a row im literally about to top myself

47. Jason Paul says: