In: Statistics and Probability
5. A driver encounters two traffic lights on the way to work
each morning. Each light is either red, yellow, or green. The
probabilities of the various combinations of colors is given in the
following table:
Second Light |
|||
First Light |
R |
Y |
G |
R |
0.31 |
0.02 |
0.18 |
Y |
0.02 |
0.03 |
0.03 |
G |
0.14 |
0.04 |
0.23 |
a) What is the probability that the first light is red?
b) What is the probability that the second light is green?
c) Find the probability that both lights are of the same color.
d) Given that the first light is red, find the probability that the second light is green.
a) What is the probability that the first light is red?
The probability that the first light is red = P( first light is Red ) = 0.31 + 0.02 + 0.18 = 0.51
b) What is the probability that the second light is green?
The probability that the second light is green = P ( second light is Green ) = 0.18 + 0.03 + 0.23 = 0.44
c) Find the probability that both lights are of the same color.
= P(R,R) + P(Y, Y) + P(G, G) = 0.31 + 0.03 + 0.23 = 0.57
d) Given that the first light is red, find the probability that the second light is green.
P( second light is green | first light is red ) = P( second light is green and first light is red ) / P( first light is red )
Let P( second light is green and first light is red ) = 0.18
P( first light is red ) = 0.51
Therefore, P( second light is green | first light is red ) = 0.18/0.51 = 18/51 = 6/17 = 0.352941