The experimental probability of an event is defined as the ratio of the number of times the event occurs to the total number of trials or observations. In this case, the event is a car entering the parking lot being black.
According to the boy's record, 10 cars were black out of a total of 10+6+9+11+9 = 45 cars that entered the parking lot.
Therefore, the experimental probability of a car entering the parking lot being black is:
Experimental probability of a black car = Number of black cars / Total number of cars
= 10/45
= 2/9
= 0.222 (rounded to three decimal places)
So, the experimental probability of a car entering the parking lot being black is approximately 0.222.