Last year the number of students who graduated with a driving licence reached 200,000,a(n) averageof 40,000 per year.还有这是average的什么用法 ,句子中有两个数字

Last year the number of students who graduated with a driving licence reached 200,000,a(n) average
of 40,000 per year.还有这是average的什么用法 ,句子中有两个数字

上年拿到驾照的毕业生数量达到20万,每年的平均数是4万.