In a 12-hour period of time, a drawbridge opens 8 times, holding traffic for 15 minutes each time. If a car approaches the bridge during this 12-hour time, find the probability that the bridge is open.

In the 12-hour period, the drawbridge is open: 8 * 15 ==120 minutes==2 hours.

Then probability is: 2 / 12 ==1 / 6