Question 1174703
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The first statement is immediate consequence of the notion/conception of the  CONDITIONAL  probability.


So,  if you know that definition of this basic conception,  the proof  (in one line)  must be clear to you.


If,  in opposite,  you don't know the definition of this basic conception,  then  LEARN  it 
from any textbook or from any  Internet source.


For example, from these my two lessons,  referred below.


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On conditional probability,  see the lessons

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=https://www.algebra.com/algebra/homework/Probability-and-statistics/Conditional-probability-problems.lesson>Conditional probability problems</A> 

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=https://www.algebra.com/algebra/homework/Probability-and-statistics/More-conditional-probability-problems.lesson>Conditional probability problems REVISITED</A> 

in this site.


Read them to develop your skills and knowledge.



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