## Conditional Probablity question math HL

Discussions for the Core part of the syllabus. Algebra, Functions and equations, Circular functions and trigonometry, Vectors, Statistics and probability, Calculus. IB Maths HL Revision Notes

### 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