Conditional Probablity question math HL

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Conditional Probablity question math HL

Conditional Probability - IB Mathematics HL – IB maths HL

How can we find the probability $P(A/B’)$ if A and B are two events such that $P(A)=0.4$, $P(B)=0.2$ and $P(A/B)=0.8$?

Thanks
lily

Posts: 0
Joined: Mon Jan 28, 2013 8:04 pm

Re: Conditional Probablity question math HL

Probability - IB Mathematics HL – IB maths HL

From conditional probability formula we have that

$P(A/B)=\frac{P(A \cap B)}{P(B)}\Rightarrow$

$0.8=\frac{P(A \cap B)}{0.2}\Rightarrow P(A \cap B) =0.8 \cdot 0.2=0.16$

Finally, we have that

$P(A/B’)=\frac{P(A \cap B’)}{P(B’)}=\frac{P(A)- P(A \cap B)}{1-P(B)}=$

$=\frac{0.4-0.16}{1-0.2}=\frac{0.24}{0.8}=0.3$

Hope these help!!
miranda

Posts: 268
Joined: Mon Jan 28, 2013 8:03 pm

Re: Conditional Probablity question math HL

Thank you!
lily

Posts: 0
Joined: Mon Jan 28, 2013 8:04 pm