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### Course: Get ready for Precalculus > Unit 8

Lesson 1: Basic theoretical probability# Simple probability: yellow marble

In order to find the probability of picking a yellow marble from a bag, we have to first determine the number of possible outcomes, and then how many of them meet our constraints. Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

- What would be the percentage of the question in the video?(28 votes)
- The answer in a percentage will be 37.5%(34 votes)

- What is the probability of me getting my mommys credit card and spending her entire bank balance on vbucks?!! Also, what is the probability of me getting my dad's credit card and spending all of his money on shiny rocks in gorrilla tag?!(15 votes)
- 0% in getting any and if you manage to there is a 100% chance you will get...(7 votes)

- how do u do probability when it says =

for example p(3 or multiple of 2)?(10 votes)- When it says p(3 or multiple of 2), it means What is the probability of getting either a 3 or a multiple of 2? To do this, you would add the probability of getting a three to the probability of getting a multiple of 2.(3 votes)

- Do we use rounding for probability?(6 votes)
- Whether we round off our answers (or our intermediate calculations) depends on the problem we're trying the solve, and the conditions we are given. For the kinds of probability calculations we are doing here (that rely mostly on counting procedures) we don't round off, as a general rule.(0 votes)

- I understand this but I need help with this question from DeltaMath "In a popular online role playing game, players can create detailed designs for their characters "costumes" or appearance. Shaniece set up a website where players can buy and sell these costumes online. Information about the number of people who visited the website and number of costumes purchased in a single day is listed below.

97 visitors purchased no costumes

26 visitors purchased exactly one costumes

13 visitors purchased more then one costume

Based on these results, express the probability that the next person will purchase more then one costumes as a percent to the nearest whole number "

If you can please help.😁(3 votes)- Well, I'm not great at this stuff, but I can at least try.

There are 136 visitors, because 97 + 26 + 13 = 136. 13 visitors purchased more than one costume, so the probability is 13/136. I personally don't understand the last part, so I can't help you there.

Hope this helped! :)

Art3mis(3 votes)

- What is the probability of a 8 sided spinner with 2 red, 3 green and, 3 blue will land on blue as percentage and, decimal?(2 votes)
- Theoretical probability gives 3/8 which is .375 as a decimal or 37.5%.(4 votes)

- To find the probability of pulling a yellow marble from the bag, you need to determine the ratio of the number of yellow marbles to the total number of marbles in the bag. In this case, there are 3 yellow marbles and a total of 8 marbles. So the probability of pulling a yellow marble is 3/8(2 votes)

- Do we use rounding for probability?(3 votes)
- Yes, you can always round your answer to a certain number of decimal places if expressing it as a decimal.(1 vote)

- I had this question on a test and couldn't figure out the answer. Maybe one of you can help me. There are marbles in a box. Two-thirds of them are white, half of them are red, and 6 of them are green. How many marbles are in the box and what is the probability of selecting a white marble?(3 votes)

## Video transcript

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.