maths probability (10m)

Q1 :P(2 white balls in box A)= P(A white ball is selected from box A and put into box B and a white ball is selected from box B and put into box A)
+
P(A red ball is selected from box A and put into box B and a red ball is selected from box B and put into box A)
= 2/(2+4) x 2/(2+3) + 4/(2+4) x 4/(1+4)= 1/3 x 2/5 + 2/3 x 4/5= 2/3 Q2 :a) No.
The possible time interval for Jane to get on a route 6C as below :
6:02 to 6:10
6:12 to 6:20
6:22 to 6:30
6:32 to 6:40
6:42 to 6:50
6:52 to 7:00All these are 8 minutes long.Total 8 x 6 = 48 minutes P(Jane gets on a route 6C) = 48/60 = 4/5
while P(Jane gets on a route 6F) = 1/5b)P(Jane gets on a route 6C bus at least once in 3 succeessive days)= 1 - P(Jane gets on a route 6F bus in 3 succeessive days)= 1 - (1/5)³= 124/125

2011-01-24 00:59:05 補充：
Oh Sorry! , I miss Q3 to Q6.