Step 1 :Given the probabilities of selling 0, 5, 10, and 20 mini cookies in a day are 0.22, 0.38, 0.14, and 0.07 respectively.
Step 2 :We know that the total probability should be 1. So we can calculate the missing probability by subtracting the sum of the given probabilities from 1.
Step 3 :Let's denote the probability of selling 15 mini cookies in a day as \(P_{15}\).
Step 4 :So, \(P_{15} = 1 - (0.22 + 0.38 + 0.14 + 0.07)\).
Step 5 :Calculate the value of \(P_{15}\).
Step 6 :\(P_{15} = 0.19\).
Step 7 :Final Answer: The probability of selling 15 mini cookies in a given day is \(\boxed{0.19}\).