traffic lights

[TomZiel]

If a person passes through 6 sets of independent traffic lights that have a probability of 0.7 to stop the person at any particular set.

Then how would you figure out the probability of that person stopping on the 2nd and 6th sets only?

[HallsofIvy]

That looks straight forward. If the probability of being stopped is 0.7, then the probability of not being stopped is 0.3. Since these events are independent, the probability of them happening together is their product. Of 6 sets of lights the person is to be stopped at a particular 2 and not at the other 4. That is:
(0.3)4(0.7)2.