Question

From a batch of 20 bricks of which 8 are defective, exactly 2 bricks are chosen, one at a time without replacement. What is the probability that the second brick chosen is defective?

Answer 1

okk
total =20
good =12
defective equal =8
so choice
first defective * second defective +first good * second defective

Answer 2

for choosing from defective 8 C 1

Answer 3

can try it now ??

Answer 4

i think it's 8/19

Answer 5

but, book says it's wrong

Answer 6

correct answet \[\frac{ 2 }{ 5 } + 0.001\]

Answer 7

look there are two choice
1) first defective * second defective
2)first good * second defective
cal probab for first and than for second and add them up

Answer 8

first defective is 8/20
second defective 7/19 right?

Answer 9

yeah now multiply it

Answer 10

first good 12/20
second defective 9/19?

Answer 11

that will be ans of first choice

Answer 12

there are only 8 defective

Answer 13

yes, thats mistypo

Answer 14

can u do it now

Answer 15

(12/20)*(8/19) +(8/20)*(7/19)

Answer 16

yes, but i really didn't understand how we got that

Answer 17

look we have to choose two bricks

Answer 18

second must be defective

Answer 19

so two choices for first brick

Answer 20

either it is good or it defective
if it is good then second is defective
if first is defective than second is defective

Answer 21

now ??

Answer 22

ohh now i get it, but why book says it's 2/5+0.001 when it is 2/5-0.001?

Answer 23

calculate properly what we calculated upto that it is correct
mistake can be in our addition or book print :P

Answer 24

ok, thank you very much :D

Answer 25

wlcme :)