Final answer:
To find the probability that it will rain on at least one of two independent days, we use the complement rule: subtract the probability that it won't rain on both days from 1 to get a 84 percent chance of rain today or tomorrow.
Step-by-step explanation:
The question of whether it will rain today or tomorrow given a 20 percent chance of rain today and an 80 percent chance of rain tomorrow can be solved using the concept of independent events in probability. Since the two events are independent, the probability that it will not rain today is 1 - 0.20 = 0.80 and the probability that it will not rain tomorrow is 1 - 0.80 = 0.20. To find the probability that it will rain on at least one of the days, we calculate the probability that it will not rain on both days and subtract it from 1. This is the complement rule. So, the probability that it will not rain both days is 0.80 * 0.20 = 0.16. Therefore, the probability that it will rain today or tomorrow is 1 - 0.16 = 0.84, or 84 percent.