average calculating operation time

例句：

1. 1. The average temperature in the city is around 20 degrees Celsius.
   这个城市的平均温度大约是20摄氏度。
2. 2. The average income of a doctor is much higher than that of a lawyer.
   医生的平均收入远高于律师。
3. 3. The average life expectancy for women in their 50s is 78 years.
   50岁女性的平均预期寿命为78年。