Thread: Dependant events help?

Question:
In a lots of 20 batteries ,4 are defective .If 2 are chosen without replacement,determine if the events D1 (event of selecting the first battery) and D2(event of selecting the second battery )are dependant.

Attempt:
4/20*15/19...

Am I correct?

Originally Posted by mj.alawami

Question:
In a lots of 20 batteries ,4 are defective .If 2 are chosen without replacement,determine if the events D1 (event of selecting the first battery) and D2(event of selecting the second battery )are dependant.

Attempt:
4/20*15/19...

Am I correct?

Your definitions of D1 and D2 make no sense. Do you mean D1 is the event that the first selected battery is defective and D2 is the event that the second defective battery is defective?

Originally Posted by mr fantastic

Your definitions of D1 and D2 make no sense. Do you mean D1 is the event that the first selected battery is defective and D2 is the event that the second defective battery is defective?

Yes,I am very Sorry that i forgot to mention those things...

So is my answer correct?

Thank you for mentioning it

Originally Posted by mj.alawami

Yes,I am very Sorry that i forgot to mention those things...

So is my answer correct?

Thank you for mentioning it

How does your answer determine whether or not D1 and D2 are independent?

My advice is to draw a tree diagram and use it to calculate Pr(D1), Pr(D2) and Pr(D1 and D2).

Then compare Pr(D1)xPr(D2) with Pr(D1 and D2).