Life expectancy expectancy, Life

raima

This is in addition to this post about "Do u get 6 to 8 hours of sleep?" by 布小熊
http://www.loyaukee.com/forum/vi ... &extra=page%3D1

Got me thinking about life expectancy
http://en.wikipedia.org/wiki/List_of_countries_by_life_expectancy

I've always known Japan is No. 1 but had no idea Hong Kong is No. 2.
They don't have the healthiest life style. Hours of sleep is definitely not 8 hours. Many work for 10-12 hours daily. I wonder why.

tofu

what is the formula for calculate the life expectancy.  
if a new born baby die, we need eight 90years person to keep the life expectancy at age 80 wor.