If the odds against event $E$ are 1 to 4 , what is the probability of $E$ ? The probability of event $E$ is (Simplify your answer.)

Step 1 ：The odds against an event is the ratio of the number of ways the event cannot happen to the number of ways the event can happen. In this case, the odds against event E are 1 to 4, which means for every 1 time the event does not happen, it happens 4 times.

Step 2 ：Therefore, the total number of outcomes is 1 (not happening) + 4 (happening) = 5.

Step 3 ：The probability of event E happening is the number of ways it can happen divided by the total number of outcomes, which is \(\frac{4}{5}\).

Step 4 ：Final Answer: The probability of event E is \(\boxed{0.8}\).