a student signs up for 3 courses for this semester. the probability of getting an a in class 1 is 0.3. the probability of getting an a in class 2 is 0.4. the probability of getting an a in class 3 is 0.5.

Question

anonymous · Answer

a) what is the probability of getting 3 As this semester?
b) what is the probability of getting 2 As this semester?
c) what is the probability of getting at least 1 A this semester?

anonymous · Answer

a) multiply the three numbers together $.3\times .4\times .5$ assuming independence

anonymous · Answer

yeah i was thinking the same thing for A but what about the others

anonymous · Answer

b) two A's you have to work by cases

anonymous · Answer

class 1, class 2, class 3 
A           A          not A          $.3\times .4\times .5$
A        not A       A               $.3\times .6\times .5$
not A    A          A                $.7\times .4\times .5$ 

find these three numbers, add them up

anonymous · Answer

c) at least on A is easiest found by computing the probability that you get exactly no A and subtract that number from 1

anonymous · Answer

*one A

anonymous · Answer

i.e. $1-.7\times .6\times .5$

anonymous · Answer

Thanks big time!