Final answer:
The probability of selecting a red cap is 0.45 or 45%.
Step-by-step explanation:
To find the probability of selecting a red cap, we need to determine the number of red caps available and the total number of caps. There are 9 red caps out of a total of 20 caps at the party. So, the probability of selecting a red cap is:
P(Red) = Number of Red Caps / Total Number of Caps P(Red) = 9 / 20 = 0.45 or 45%