## mariomintchev 2 years ago 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.

1. mariomintchev

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?

2. satellite73

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

3. mariomintchev

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

4. satellite73

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

5. satellite73

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

6. satellite73

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

7. satellite73

*one A

8. satellite73

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

9. mariomintchev

Thanks big time!