Question 1011823
.4 * .4 * .4 = .064
there is a 6.4% probability that all lights will be green when she encounters them.


if you think about it as percentages, and assume that she does a tally over 1000 trips to school, then you can think about it as follows:


40% of the rime the first light will be green.
that's 400 trips out of 1000.


in those 400 trips that the first light was green, the second light will be green 40% of the time for a total of .4 * 400 = 160 times.


in those 160 times that the first and second light was green, the third light will be green 40% of the time for a total of .4 * 160 = 64 times.


64 times out of a thousand = 64 / 1000 = .0064 = 6.4%.