Conditional Probability Traffic light question

[Pure Canuck]

Hey guys Me and my friend just got this question and it seems easy but i just want to make sure we are right anyway here it is:

A road has two stoplights at consecutive intersections. The prob. of a red at the first is 0.55 and the probability of a green at the second, give a green at light oine is .75

Find the prob of a green at both intersections:
Givens = (r1 = .55) (g2|g1=.75)
now i believe its simply as just r1*.75.

which is like .33

Anybody know if i did this right?

Thanks

 

[*melinda*]

In your problem statement:

P(r_1 )=0.55 and P(g_2 |g_1 )=0.75

but I don't know how you got your answer because .55*.75 = .4125, though I do agree that .33 is very close to the answer, depending on how you round the decimal.

 

[iNCREDiBLE]

Hint: http://mathworld.wolfram.com/ConditionalProbability.html" .
Just use the formula.