Exercise 2: sample answer

From 325 to 1582 is 1,257 years. Dividing by 128 gives about 9.8 days, so roughly ten days of error (check the figure). That matches the ten days removed in 1582, which is no coincidence: the reform was designed to put the spring equinox back to the date it had at the time of the Council of Nicaea in 325 (check). The slight difference between 9.8 and 10 comes from rounding the 128-year figure and from the way the reformers counted.