# Two probability questions. Even HOW to do it would be a huge help

#### SteffiB

##### New Member
1.Mary has two friends, Ann and Sarah. Mary will visit Ann this evening if the 19A bus arrives before 6PM. Otherwise, She will visit Sarah. The probability of the 19A bus arriving before 6pm is 40%. If she visits Ann, the probability that Ann will be at home is 10% and if she visits Sarah, the probability that Sarah will be home is 20%. Find the probability that the friend Mary visits will be home

2.A darts player finds that on average he hits the bullseye 4 times out of 5. Calculate the probability that in a random sample of 4 shots, he will miss the bullseye at least 3 times

#### Dason

Do you know the law of total probability?

Do you know if the binomial distribution?

#### SteffiB

##### New Member
Do you know the law of total probability?

Do you know if the binomial distribution?
I know the general binomial distribution and applied in to the darts question but didn't get the right answer. Can you expand on the law of total probability please?

#### Dason

Can you show what you did for the second question, the answer you got, and what you think the correct answer is?

#### SteffiB

##### New Member
Can you show what you did for the second question, the answer you got, and what you think the correct answer is?
n= no of trials=4
p=probability of success=0.2
q=probability of failure=0.8
x=no of successes in n trials=3 or 4
P(x<=4, but>=3)=P(x=4)+P(x=3)
=(4C4 x (0.2)^4 x (0.8)^0)+(4C3 x (0.2)^3 x (0.8)^1))
=(0.1667x0.0016x1)+(2x0.008x0.8)
=0.013