A company records the number of angry calls made to a particular department every working day. It then takes the average of these numbers over 10 working days. This average is based in the assumption that the distribution of the number of angry calls on a particular day is unaffected by the day on which the call is received. The probability that this average is greater than 25 is 5%. Calculate the mean number of angry calls on any particular day if you know that the standard deviation of the number of angry calls per day is 10. You may find this standard normal table useful. Give your answer to 3 decimal places. Mean number of angry calls per day =