Question

among 10 laptop 5 are good and 5 have defects .unaware of this a customer buys 6 laptops
(a) what is the probability that exactly two of them are defective
(b)given that atleast 2 purchases laptops are defective,what is the probability that exactly 2 are defective?

Answer 1

(a) : 0.32

Answer 2

could plz explain it step by step ? thanks

Answer 3

5/10x4/9x3/8x2/7x5/6x4x5

Answer 4

the probability of defective among 6 purchased would be 5/6 .m stuck how do i find the exact two in the A part

Answer 5

probability that 4 will be good ones 5/10x4/9x3/8x2/7 ...x probability that 2 will be defectve 5/6x4x5

Answer 6

at least two defective => more than two defective

Answer 7

"5/10x4/9x3/8x2/7"
here why did u write 5/10? we need to select defective laptops out of 6 i.e 6 are purchased.not from total laptops

Answer 8

customer buys 6 laptops .... two exactly defective means ... 4 must be good one and 2 must be bad one.

Answer 9

okay i will ask you a question ... what is the change that 1st laptop will be non-defective?

Answer 10

u mean chance? it would be 5/6 because 6 are total purchased and 5 are defective among them

Answer 11

sorry it would be 1/6

Answer 12

no ... 5/10

Answer 13

because ... you have five good laptops out of then ... your change of picking good laptop will be 5/10

Answer 14

another question: if you have to choose two laptops, what is the probability that you will get both of good laptops

Answer 15

umm....i think it would be 5/10?

Answer 16

m sorry i reall suck in probability :(

Answer 17

no ... it's 5/10x4/9

in first draw, you have 5 good laptops out of 10
int second draw, you have 4 out of 9,

similarly find the probability of getting 4 laptops out of 10, good ones

Answer 18

alright i understood now

Answer 19

and after that, find the probability of getting 6 laptops : 4 good and 2 damaged

Answer 20

probability of 4 out of 10 ,good ones will be = 5/10X 4/9 X 3/8 X 2/7..m i right?

Answer 21

yeah ... now add two bad ones at the end ... that will give you the probability of getting exactly 2 bad ones

Answer 22

prob of 2 damaged out of 6 =2/6X 1/5

Answer 23

ok got it .thanks

Answer 24

no ... it's 5/6x4/5

remember, we haven't gotten damages ones in 4 draws

Answer 25

but m confused about one thing that why u add both prob at the end

Answer 26

not adding ... multipling

Answer 27

oh yes ok

Answer 28

thanks for the testimonial spd ... i will give you a hint to solve the second question

it assumes that you have atleast 2 defective out of 6, now just focus on that word AT LEAST

it means you can have 2 defective or 3 defective or 4 defective or 5 defective laptops,

calculate the probability of exactly getting all above defective laptops individually and add them.

the probability go exactly 2 defective out of atleast 2 is

answer of A/(the sum of probability of individuals from above)