Answer: 9.83
Step-by-step explanation:
The first step is to add up all the values given:
11.01 + 10.50 + 5.70 + 14.67 + 9.50 + 12.54 + 8.90 + 13.56 + 11.23 + 6.80 + 3.00 + 10.55 = 117.96
Then we divide this sum over n = 12 since this is the sample size given (i.e. the number of customers)
117.96/n = 117.96/12 = 9.83