Over the years, the mathematical problems in the postgraduate entrance examination are 20 18, 20 16, 202 1, 2020, 2009, 2007, 20 14, 2008, 20 17, 2008. It can be seen that the easiest year from 2003 to 2 1 is 201,and the most difficult year is 20 18. ?

Expansion: Generally speaking, the higher the average score of the test paper, the lower the difficulty of the test paper. On the contrary, the lower the average score of the test paper, the more difficult it is. The following figure is arranged in ascending order of the average score of mathematics for three years:

Sorting out the three difficulties in mathematics for postgraduate entrance examination over the years

One's deceased father grind mathematics, mathematics, mathematics three-year average score as shown in the figure below:

Average score of graduate students in mathematics over the years