Question

Three CDs are picked at random from a collection of 13 CDs of which six are defective. Find the probability of the following events. (Round your answers to three decimal places.)

(a) All three CDs are defective.



(b) All three CDs are functioning properly.

Answer 1

How many ways are there to select 3 defective CDs?

Answer 2

@jim_thompson5910 yes

Answer 3

I'm asking for a number. Re-read what I asked above.

Answer 4

I was thinking (13!)/(10!) but that just seems off

Answer 5

there are 6 defective CDs and 3 slots

n = 6
r = 3


n C r = (n!)/(r!*(n-r)!)

6 C 3 = (6!)/(3!*(6-3)!)

6 C 3 = ???

Answer 6

I'm using n C r instead of n P r because order doesn't matter

Answer 7

So if we do the 6 C 3 I receive the value of 20

Answer 8

good

Answer 9

how many ways are there to select 3 CDs (defective or nondefective, it doesn't matter)

Answer 10

So n = the total amount and r = the possible ways ?

Answer 11

yeah if you had 5 people and 3 seats, then n = 5 and r = 3

Answer 12

how many ways are there to select 3 CDs (defective or nondefective, it doesn't matter) ?

Answer 13

13 = n

Answer 14

then 6-3 = r?

Answer 15

r = number of slots

Answer 16

r = 3 slots

Answer 17

I use the same formula correct?

Answer 18

yes use the n C r formula

Answer 19

3 C 6 or 3 C 13 ( I apolgize as I am trying to learn :( )

Answer 20

apologize *

Answer 21

n = 13
r = 3

n C r = 13 C 3 = ??

Answer 22

Rule: the value of r cannot be larger than the value of n

Answer 23

286 ... so again n would = 13 because thats the total of CDS and because we want 3 CDS and it doesn't matte if there defective or not. That is how we get to 13 C 3

Answer 24

yes, there are 286 ways to pick 3 CDs from a pool of 13 (order doesn't matter)

Answer 25

So the probability of picking 3 defective is 20/286 = 10/143

Answer 26

try out part b and tell me what you get

Answer 27

i am sorry where did you receive the 20? from 20/286

Answer 28

I will try part B thanks!

Answer 29

from

n C r = 6 C 3 = 20

Answer 30

Okay so if 6 are defective then they're 7 good ones

Answer 31

so would it be 7 C 3

Answer 32

then that answer = 35

Answer 33

so far, so good

Answer 34

we don't use 286 right it wouldn't be 35/286

Answer 35

Wait yeah. we use 286 because it is still 13 C 3

Answer 36

Yes !! it is ! omg I get it now. so C = choice ...so n will always = the amount that you have then r will be what you are looking for however like you said r will never be bigger than N

Answer 37

@jim_thompson5910 you are a life saver !!

Answer 38

C stands for combination to be more precise

compared to the P for permutation in n P r

http://www.regentsprep.org/regents/math/algtrig/ats5/lcomb.htm

Answer 39

@jim_thompson5910 thank you I will check out that link YOU ARE the BEST

Answer 40

I'm glad I could help out

Answer 41

@jim_thompson5910 I wil try to use this for the rest of my questions. thanks again!