Question

I need help with a probability question.. look at the screenshot in the comments :)

Answer 1

it's number 22

Answer 2

@nincompoop

Answer 3

Ok. Let's start with choice # 1 and #3.
Both of them are with replacements, right?

Answer 4

right

Answer 5

With replacements means that each time, you pick out of the total number of marbles, which is 5

Answer 6

1 blue
2 white
2 red

Answer 7

P(red and red)

Answer 8

First of all, what is the probability that you pick a red marble?

Answer 9

2/5 right?

Answer 10

Right.
Now, let's say you picked out a red marble.
Since there IS replacement, you have to put it back and pick again.

Answer 11

okay..

Answer 12

Since we have to pick red, put it back, then pick red again, the probability is...
P(red)*P(red)=(2/5)*(2/5)=(4/25)
In percent, it would be 16%

Answer 13

OH! I understand now.. you just take the probabilities and multiply them?

Answer 14

Yes. Now, try number 3

Answer 15

ok so the probability of blue is 1/5 and the probability of red is 2/5. so that would be 2/25 which reduces to 0.08, which is 8%

Answer 16

Correct!

Answer 17

Now, what you have to be careful of is that this only works for probability WITH replacement.

Answer 18

For probability without replacement, the method is different.

Answer 19

P(white and white)

Answer 20

What is P(white)?

Answer 21

2/5

Answer 22

Good.
Now listen carefully.
Let's say you picked out one white.
Because it's WITHOUT replacement, you don't put the marble back.
How many are there left after you picked white?

Answer 23

1

Answer 24

total amount of marbles

Answer 25

4 now, right?

Answer 26

Right. So there is one white marble out of 4 marbles, right?

Answer 27

yes, 1/4

Answer 28

The first probabilty=2/5
The second probability=1/4
(2/5)*(1/4)=1/10 or 10%

Answer 29

If you understand this, try number 4

Answer 30

the probability of white is 2/5 and red is 2/5. would you multiply 1/4 and 1/4 together?

Answer 31

Not quite..

Answer 32

When you pick the first time, the total number of marbles is 5.
When you pick the second time, the total number of marbles is 4 since you already picked...

Answer 33

so 2/5 * 1/4?

Answer 34

Read the question: P(white and red)
Number of white marbles doesn't affect number of red marbles.

Answer 35

so what am I supposed to do? I know the answer is 20%

Answer 36

P(white)=2/5
P(red)=2/4 because there are 2 red marbles out of 4 marbles
P(white and red)=2/5*2/4=1/5 or 20%

Answer 37

Confused?

Answer 38

no I took notes lol, but I understand now. thank you very much!