13. A bag contains 3 red balls and 4 white balls. Two balls are drawn one after the other without
replacement at random from the bag. If the second ball drawn is given to be white, what is the
probability that the first ball drawn is also white?
[CBSE Sample Paper 2003]
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Step-by-step explanation:
no of total balls = no. of red balls +no.of white balls
=3+4
= 7
when 2 balls are drawn without replacement =7-2=5
if 1st ball is white,then no. of white ball remaining= 4-1=3
P(E) = no. of white balls remaining
----------------------------------------
total no. of balls in bag
= 3
------
6
= 1
----- or 0.5
2
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