Data Sufficiency

Dear All,
I am quite difficult to choose intelligently which is the best one. please help me!

Q2:
On Saturday morning, Malachi will begin a camping vacation and he will return home at
the end of the first day on which it rains. If on the first three days of the vacation the
probability of rain on each day is 0.2, what is the probability that Malachi will return
home at the end of the day on the following Monday?
A. 0.008
B. 0.128
C. 0.488
D. 0.512
E. 0.640

Thanks a lot.
William,

NSNguyen wrote:Dear All,
I am quite difficult to choose intelligently which is the best one. please help me!

Q2:
On Saturday morning, Malachi will begin a camping vacation and he will return home at
the end of the first day on which it rains. If on the first three days of the vacation the
probability of rain on each day is 0.2, what is the probability that Malachi will return
home at the end of the day on the following Monday?
A. 0.008
B. 0.128
C. 0.488
D. 0.512
E. 0.640

Thanks a lot.
William,

Well, for him to return on monday, it should not rain on saturday and sunday and it should rain on monday ..

If the probability of it raining is 0.2, then probability of not raining is 1-0.2 = 0.8 ..

So, the probability according to the theorem of multiplication of probabilities (btw this is a example of conditional probability) = 0.8*0.8*0.2 = 0.128 .. that is B

Regards