The average number of five numbers is 9. If one of them is changed to 1, then the average number of the five numbers is 8. What is the changed number

The average number of five numbers is 9. If one of them is changed to 1, then the average number of the five numbers is 8. What is the changed number

9 × 5-8 × 5 = 45-40 = 51 + 5 = 6