Lazar drives to work every day and passes two independently operated traffic lights. The probability that both lights are green is 0.41. The probability that the first light is green is 0.59. What is the probability that the second light is green, given that the first light is green?

0.71

0.69

0.67

0.73

Question

Lazar drives to work every day and passes two independently operated traffic lights. The probability that both lights are green is 0.41. The probability that the first light is green is 0.59. What is the probability that the second light is green, given that the first light is green?

 0.71

 0.69

 0.67

 0.73

rebeccaxhawaii · Answer

@phi

phi · Answer

Pr(a | b) = Pr( a and b) / Pr(b)

phi · Answer

does that ring any bells ?

foxesrcool · Answer

69 Is a geuss

phi · Answer

Pr (2nd light green |  1st light is green) = Pr(both green) / Pr(1st light is green)

the numbers you need are given in the problem

rebeccaxhawaii · Answer

phi this always confuses me. i hate probability.

foxesrcool · Answer

Me too.

rebeccaxhawaii · Answer

@phi

phi · Answer

what is the probability both lights are green ?

rebeccaxhawaii · Answer

0.41

phi · Answer

ok, and what is the probability the first light is green ?

rebeccaxhawaii · Answer

0.59

phi · Answer

now we use the formula
Pr (2nd light green |  1st light is green) = Pr(both green) / Pr(1st light is green)

putting in the numbers:
Pr (2nd light green |  1st light is green) = 0.41 / 0.59

rebeccaxhawaii · Answer

ohhh thats it? it equals 0.41/0.59?

phi · Answer

yes

rebeccaxhawaii · Answer

oh okay. just me over complicating things again but thanks c: