IIT JEE , AIEEE Forum - Mathematics , Algebra

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1. if P(not B)=0.65,P(AUB)=0.85,find P(A) if A and B r independent events?

2. if A & B r independent events such that P(AUB)=0.60,P(A)=0.2,find P(B)?

3. there are 3 red and 5 black balls in bag A ; 2 red and 3 black balls in bag B ; one ball is drawn from bag A and two from bag B. find the probability that out of 3 balls drawn one is red and two are black?

somebody plz solve this.

raulrag009

thanks man!!!!!!

edited

priyesh

q1)

P(A

B) = P(A) + P(B) - P(A

B)

now since A & B are independent P(A

B) = P(A)P(B)

P(A

B) = P(A) + P(B) - P(A)P(B)

P(AUB) & P(B) is given as 0.85 and 1- .65 = .35 so P(A) can be easily calculated from above equation

Q2) similar

Q3) two cases are possible

from A red is drawn ,and from B two black are drawn

prob of this case = 3/8 * 3/5 * 1/2

from A black is drawn from B one red one black is drawn

prob of this case = 5/8 * 2/5 * 3/4

so total prob =prob(case 1) + prob(case 2) = 3/10

priyesh

@ raulrag

u've written

As A and B are independent P(A

B)=0

dude this condition is for exhaustive events

for independent events P(A

B) = P(A)P(B)

sboosy

Priyesh is spot on
p(A union B)=p(A)+1-p(not B)-p(A)[1-p(not B))
0.85=0.35+P(a)(0.65)
p(A)=10/13

akhil_o

3.)

case 1- R from A, 2Bl from B

case 2-B from A, RB from B

so we have

P=[(3/8)(3/5)(2/4)]+(5/8)[(2/5)(3/4)+(3/5)(2/4)]

=39/80

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